breastfeeding.pdf

Developmental Review 28 (2008) 503–521

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Developmental Review

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / d r

Breastfeeding and the mother–infant relationship—A review

Jarno Jansen *, Carolina de Weerth, J. Marianne Riksen-WalravenDepartment of Developmental Psychology, Behavioral Science Institute, Radboud University Nijmegen, P.O. Box9104, Nijmegen 6500 HE, The Netherlands

a r t i c l e i n f o

Article history:Received 9 July 2008Available online 15 August 2008

Keywords:BreastfeedingMaternal bondInfant attachmentMother–infant relationshipOxytocinProlactin

0273-2297/$ - see front matter � 2008 Elsevier Indoi:10.1016/j.dr.2008.07.001

* Corresponding author.E-mail address: [email protected] (J. Jansen).

a b s t r a c t

A positive effect of breastfeeding on the mother–infant relation-ship is often assumed in the scientific literature, but this has notbeen systematically reviewed. This review aims to clarify the roleof breastfeeding in the mother–infant relationship, which is con-ceptualized as the maternal bond toward the infant and infantattachment toward the mother. Our findings indicate that theoret-ical mechanisms through which breastfeeding may enhance thematernal bond or infant attachment (i.e., endocrine and sensoryfactors involved in breastfeeding) can be found in both humansand animal models. However, the few empirical studies investigat-ing this association have not found convincing support for a rela-tion between breastfeeding and the quality of the mother–infantrelationship. We therefore conclude that assumptions on a positiverole of breastfeeding on the mother–infant relationship are notsupported by empirical evidence, and recommendation of breast-feeding should solely be based on its well-documented positiveeffects on infant and maternal health.

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Introduction

Lactation is a defining characteristic of all mammals. In humans, breastfeeding has been related toimproved maternal health (Labbok, 2001) and improved health and development of the infant (Ander-son, Johnstone, & Remley, 1999; Caspi et al., 2007; Hanson, 1998). The positive effects of breastfeedingon the mother–infant relationship have also been widely advocated. This relationship can be envi-sioned as consisting of two complementary facets: the maternal bond, or the mother’s tie to her infant,and infant attachment, defined as the infant’s tie to its caregiver.

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504 J. Jansen et al. / Developmental Review 28 (2008) 503–521

Claims that breastfeeding positively affects the maternal bond and/or infant attachment have beenput forward by various authors, not always accompanied by references or empirical evidence support-ing such a claim. For example, a review on the benefits of breastfeeding concludes that ‘‘. . .breastfeed-ing enhances maternal–child attachment. . .” (Anholm, 1986, p. 8) without citing any scientific worksrelating breastfeeding to the maternal bond or infant attachment. More recent publications have madesimilar statements without providing empirical evidence (Aguayo, 2001; Leung & Sauve, 2005; Misri,Kostaras, Fox, & Kostaras, 2000). Furthermore, mothers report choosing breastfeeding over bottle-feeding to improve the mother–infant relationship (Arora, Mcjunkin, Wehrer, & Kuhn, 2000; Gijsbers,Mesters, Andre Knottnerus, Legtenberg, & van Schayck, 2005). These types of claims and beliefs mayhave an important psychological impact on mothers who are unable to nurse (due to, for instance,breast surgery or jaw malformation of the infant). In these mothers, assumptions of the positive effectsof breastfeeding on the mother–infant relationship put forward by scientists and nursing staff can in-duce feelings of guilt (Crouch & Manderson, 1995; Zetterström, 1999). In fact, a UK study reported thatmothers intending to bottle-feed were, according to self-reports, likely to be charged with being a badmother (Murphy, 1999). Given these possible psychological consequences for non-breastfeedingmothers, the importance of sound scientific evidence on the relationship between breastfeedingand the mother–infant relationship becomes all the more apparent.

This review aims to clarify the role of breastfeeding in the (development of) the mother–infantrelationship. We commence by summarizing current knowledge on the concept, development, andassessment of the maternal bond and infant attachment. We then theorize how endocrine and sensoryfactors involved in breastfeeding may enhance the maternal bond or infant attachment. We summa-rize and evaluate the empirical studies on the relations between breastfeeding and the maternal bondand infant attachment. We finish this review with a discussion on general methodological problemsand possible future directions for studying breastfeeding and (the development of) the mother–infantrelationship.

The mother–infant relationship: The maternal bond and infant attachment

The maternal bond and infant attachment: Definitions

We consider the mother–infant relationship as consisting of two complementary facets: the mater-nal bond, or the tie from mother to infant, and infant attachment, or the tie from infant to mother.Infant attachment entails the tie between infant and mother that develops from a distinct innatebehavioral system, promoting mother–infant proximity (Bowlby, 1969/1982). The definition of thematernal bond is less clear. Klaus and Kennell (1976) introduced the term ‘maternal bonding’, definedas a biologically based emotional investment in the infant. After its introduction, the term ‘bonding’and the related theories on it have received a fair amount of criticism (see next section). To preventany confusion between the concept of the maternal bond and the theories related to ‘bonding’, we willhereafter refer to the tie from mother to infant as ‘the maternal bond’. Recent descriptions emphasizethat the maternal bond is complementary to infant attachment, functioning to ensure maternal close-ness to her infant (Maestripieri, 2001a). It is directed to a specific infant (Kendrick et al., 1997; Ke-verne, 2006), and it is characterized by the expression of a clearly defined set of maternal behaviors(Levine, Zagoory-Sharon, Feldman, & Weller, 2007). We propose a combination of these definitionsand define the maternal bond as the tie from mother to infant that promotes maternal behaviorsaimed at mother–infant proximity and caregiving. It develops from the distinct neurobehavioral cir-cuitry underlying emotion and motivation (e.g., Leckman et al., 2004; Swain, Lorberbaum, Kose, &Strathearn, 2007).

The maternal bond and infant attachment: Background

The maternal bond was described by Klaus and Kennell (1976) as part of a research line thatevolved mostly in response to the emerging medical procedures surrounding birth. Based on studiesin ungulates and at-risk human populations, they proposed that a mother is biologically primed to

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form an enduring emotional bond with her offspring. Furthermore, an essential part of their theoryposed that a critical period exists for this bond to develop. The theory on a critical bonding periodwas heavily criticized because of its suggested homology with animal studies, flawed methodology,and overestimation of the permanence of the putative effects (Lamb, 1982; but also read Korsch,1983; Lamb, 1983a, 1983b; Sugarman & Goldberg, 1983 for an interesting impression of the debateon the ‘‘bonding phenomenon”). Thus, although during the 1970’s many articles on bonding, and morespecifically, the existence of a critical bonding period, appeared in respected pediatric and medicaljournals (e.g., De Chateau, 1976; Grossman, Thane, & Grossman, 1981; Klaus et al., 1972; Ringler, Ken-nell, Jarvella, Navajosky, & Klaus, 1975), ‘‘by the early 1980’s, research on the bonding of mothers andtheir newborns had been dismissed by much of the scientific community” (Eyer, 1992; for reviews onthe research on a critical bonding period, see Lamb & Hwang, 1982; Myers, 1984).

Although research on the benefits of early post-partum contact was largely forgotten as a scientificarea of interest after the 1970’s, with the realization that social bonds promote survival (Carter & Ke-verne, 2002; Miller, Feldman, & Pasta, 2002), and that maternal caregiving, by providing protectionand nurturing, allows a longer period of (brain) development, research on the maternal bond and fac-tors affecting its development has more recently been renewed (e.g., Feldman, Weller, Leckman, Kuint,& Eidelman, 1999; Leckman et al., 2004). However, unlike the bonding research in the 1970’s, Feldmanand colleagues focus their research on ‘‘a clearly defined set of maternal post-partum behaviors thatemerge or intensify during the bonding stage” (Levine et al., 2007), and more clearly theorize on andinvestigate the biological basis of the maternal bond (e.g., Leckman et al., 1999; Leckman et al., 2004;Levine et al., 2007).

One of the major features of the attachment theory is the concept of attachment as an innatebehavioral system with the biological function of protection that has been built into humans andother primates through natural selection (Bowlby, 1969/1982). The attachment behavioral systempredisposes infants to display attachment behaviors (such as crying, smiling, vocalizing, approach-ing, and following) that serve to increase proximity to the caregiver, particularly in times ofdistress.

Infants become attached to caregivers with whom they regularly interact and whom they can re-sort to in times of distress. Only if no opportunity for ongoing interaction with a specific caregiver ex-ists, will there be a failure to attach, such as in the case of some institutionalized children (O’Connor,Bredenkamp, & Rutter, 1999). Although an infant forms one primary attachment (usually to themother), it may also become attached to other caregivers, such as the father, grandparents or non-familial caregivers (Ahnert, 2006; Hrdy, 1999).

Whereas nearly all infants become attached to their primary caregivers, not all are securely at-tached. A securely attached infant is able to use the caregiver as a secure base for exploration andthe attachment figure functions as the ‘outer ring’ of homeostasis for the infant, acting as a bufferagainst distress (Ahnert, Gunnar, Lamb, & Barthel, 2004; Bowlby, 1973; Spangler & Grossman,1993). When distressed, the secure infant quickly and effectively seeks contact with the caregiverand remains in contact as long as needed; after reassurance, which mostly does not take long, the se-curely attached infant contently returns to play. Insecurely or anxiously attached infants, on the otherhand, cannot use their caregiver as a secure base for exploration; they resist or avoid contact with thecaregiver, and it takes longer for them to recover from distress and return to exploration than for se-curely attached children (for a description of different types of insecure attachment, see Ainsworth,Blehar, Waters, & Wall, 1978; Main & Solomon, 1990).

Longitudinal research has shown that the security of an infant’s attachment to a caregiver is asso-ciated with the history of its interactions with that caregiver. Securely attached children have beenfound to have caregivers who sensitively and consistently respond to the children’s attachment behav-iors (De Wolff & Van IJzendoorn, 1997; Nievar & Becker, 2008; Van den Boom, 1994). Infants with inse-cure attachment relationships, on the other hand, have not experienced consistent availability andcomfort from their caregivers when distressed. Instead, they have experienced unresponsiveness,intrusiveness, rejection, or unpredictable and frightening behavior on the part of their caregivers,which makes them anxious about the availability of the attachment figure and leads to angry, avoid-ing, or disorganized behavior when experiencing distress in the presence of the caregiver (Weinfeld,Sroufe, Egeland & Carlson, 1999).


The maternal bond and infant attachment: Development

The maternal bond and infant attachment develop over time. Concerning the maternal bond, Millerand Rodgers (2001) propose that the ‘nurturant bonding system’ that promotes care to infants, devel-ops around puberty, in tandem with sexual development, and continues to develop through adult life.Although this system does not promote directing care at a specific infant, and thus does not constitutea maternal bond, it is important because one of the most important factors predicting proper maternalcaregiving and motivation would be experience in caregiving (Fleming, 2006). Thus, although devel-opment of the maternal bond by definition cannot start before pregnancy, it may be stimulated bycaregiving experience prior to pregnancy (e.g., Hrdy, 2006). Regarding the maternal bond, Winnicott(1975) already suggested how ‘‘primary maternal preoccupations” began at the end of pregnancy andcontinued through the first months after birth. Klaus and Kennell (Klaus & Kennell, 1983; Klaus, Ken-nell, & Klaus, 1995) state that the bonding process starts during pregnancy and continues to developthroughout the first years. Although this theory has, according to Tessier et al. (1998, p. 18), ‘‘with-stood the test of time”, experimental support has so far been little (see Maestripieri, 2001b). Whilecircumstantial evidence provided by the ‘La Maternité’ experiment indicates that a mandatory post-partum caregiving period in at-risk mothers may promote maternal motivation (as noted in Fuchs& Knepper, 1989), others have found that the development of the maternal bond is far from inevitable.Corter and Fleming (2002) review evidence that pre-birth maternal motivation may not be experi-enced by all mothers. Feldman et al. (1999) provide evidence that formation of the maternal bondmay be hampered by impending loss and Leckman et al. (1999) found that aspects of the maternalbond (maternal preoccupation) intensified after birth but then declined after 3 months. Evidence ofa fMRI study by Swain et al. (2004), supports the findings by Leckman et al.: in primiparous mothersthe brain response to infant crying changes. The response indicative of alarm decreases during the firstmonths post-partum, but it is replaced by a response indicative of social engagement, suggesting thatrather than weakening after three months, the maternal bond develops and changes in form.

Regarding infant attachment, in the first few weeks after birth, a period termed the ‘‘pre-attach-ment phase” by Ainsworth et al. (1978, p. 23), babies orient and signal to people without discrimina-tion of figure (Bowlby, 1969/1982). Soon thereafter, during ‘‘attachment-in-the-making” (Ainsworthet al., 1978, p. 24), they begin to show discrimination in directing their various attachment behaviorsto different figures, and these figures may also differ in how readily they can terminate an attachmentbehavior, such as crying. By the end of the first year of life, most babies have formed a ‘‘clear-cutattachment” (Ainsworth et al., 1978, p. 25) to one or more specific caregivers; they not only show sim-ple preference of these figures over others, but also actively seek and maintain proximity and contactwith their attachment figures and react with distress to separation (Bowlby, 1969/1982). Although aclear-cut attachment has been formed at the end of the first year, attachment security can change dur-ing infancy, childhood, and adolescence when the family environment changes (Thompson & Raikes,2003; Waters, Weinfeld, & Hamilton, 2000).

Taken together, our initial definition of the maternal bond suggests that it may bear many similar-ities to infant attachment. We emphasize, however, that although both concepts share aspects relatedto cause (innateness, neurobehavioral origin; Insel, 1997; Miller & Rodgers, 2001) and effect (promot-ing survival of the offspring), both differ in their behavioral output (seeking vs. offering care), and maydiffer in their developmental trajectory. Whereas it is clear that infant attachment develops during thefirst year, and may change when the family situation is altered, we know very little about the devel-opment of the maternal bond. Clearly, more research is needed to further elucidate the processes in-volved in the development of the maternal bond.

The maternal bond and infant attachment: Scientific assessment tools

Psychological research on the dyadic mother–infant relationship has mainly focused on infantattachment, yielding a number of scientific assessment tools, while the available methods to investi-gate the maternal bond are limited.

The emotional aspect of the maternal bond has been assessed through questionnaires, e.g., theParental Bonding Questionnaire (PBQ: Brockington et al., 2001) or the Parenting Stress Index (PSI:


Abidin, 1986), self-report (e.g., Wojnar, 2004), or structured observation (e.g., Cernadas, Noceda, Bar-rera, Martinez, & Garsd, 2003; Martone & Nash, 1988). All of these approaches have benefits and prob-lems that may affect the outcome, and none has been used in more than a handful of studies to studythe maternal bond. For example, the PSI has been widely used to assess parenting stress, but to ourknowledge, only one study has used it to specifically assess the maternal bond (Else-Quest, Hyde, &Clark, 2003).

In attachment research, the Strange Situation Procedure (SSP, Ainsworth et al., 1978) is by far themost widely used procedure to assess the quality of the attachment between infant and caregiver (Sol-omon & George, 1999). The SSP is a structured 20-min laboratory procedure designed to assess bymeans of observation whether infants use the caregiver as a secure base under conditions of moderatebut increasing stress, such as the entrance of a stranger and separation from the caregiver. Based ontheir behavior during the SSP, infants are classified into one of four attachment categories, one‘‘secure” category (B), and three different ‘‘insecure” categories (A, C, and D). In a review on the originsof attachment theory, Bretherton (1992, p. 767) notes that ‘‘it often seemed as if attachment and theStrange Situation had become synonymous”. The SSP however is not a paradigm suitable for determin-ing attachment security in all populations. Due to its stressfulness it is less useful for use in clinicalpopulations that are vulnerable to stress (such as depressed mothers and their infants) and the pro-cedure may be too stressful in cultures where caregiver–infant separations are uncommon. Further-more, the SSP is designed for use in infants between the age of 12 and 24 months.

To overcome some of these limitations, Waters and Deane (1985) designed the Attachment Q-Set(AQS) that assesses the security of the infant–caregiver attachment relationship in the (non-stressful)home setting. The AQS can be used in children from 12 to 60 months and consists of 90 cards describ-ing specific behavioral characteristics of children. After having observed the infant for an extendedperiod of time, a trained observer sorts the cards into nine stacks, ranging from ‘most descriptive ofthe child’ to ‘least descriptive of the child’. A security score ranging from�1.0 (prototypically insecure)to +1.0 (prototypically secure) can subsequently be calculated by correlating the child’s profile withthat of a prototypically secure child as provided by experts in the field (Waters & Deane, 1985). Ina large meta-analysis of 139 AQS studies, Van IJzendoorn, Vereijken, Bakermans-Kranenburg, and Rik-sen-Walraven (2004) concluded that the AQS shows sufficient validity to be considered an appropriatemeasure of the attachment security of infants and toddlers.

Theoretical support for a role of breastfeeding in the mother–infant relationship

Breastfeeding differs from bottle-feeding in a variety of ways. The hormones that stimulate milkproduction and milk ejection have, in animal models, been shown to affect maternal caregiving behav-ior and pair bonding. Furthermore, non-nutritive features of the mother–infant interaction duringbreastfeeding may promote infant attachment. Thus, breastfeeding may, in theory, affect the maternalbond or infant attachment.

In this section, we will discuss how factors inherent to breastfeeding may promote the maternalbond and infant attachment. We will focus on two potential mechanisms: effects of breastfeedingon the maternal bond by the hormones involved in breastfeeding, and effects of breastfeeding on in-fant attachment by non-nutritive aspects associated with a typical mother–infant breastfeedinginteraction.

Breastfeeding and hormones: Potential effects on the maternal bond

Breastfeeding affects the endocrine system of the mother (for a review, see Buhimschi, 2004). Spe-cifically, the small peptide hormone oxytocin (OT) is released in a pulsatile fashion in response to suck-ling (Nissen et al., 1996; Ueda, Yokoyama, Irahara, & Aono, 1994, but see Uvnäs-Moberg, 1998, for areview). OT stimulates the contraction of smooth muscle cells and the release of milk from the mam-mary gland. Prolactin (PRL), another peptide hormone, stimulates milk secretion in mammary tissue(Neville, McFadden, & Forsyth, 2002) and is released after suckling (Johnston & Amico, 1986). Theendocrine response to breastfeeding primarily serves to support milk production, but animal research


has shown that it may play an essential role in promoting the maternal bond (as reflected by theoccurrence of maternal caregiving behavior). In the following sections, we will briefly review studiesexamining the role of oxytocin and prolactin in maternal caregiving behavior and the maternal bond.

OxytocinOT can potentially affect the maternal bond. Kendrick (2000) reviewed the effects of OT on mater-

nal caregiving behavior in animals and suggested that OT both activates behavior beneficial for infantsurvival and suppresses behavior that might harm the offspring. Due to the fact that bond formation issaid to occur in situations in which OT plays a critical role, such as parturition, OT was already sug-gested to regulate social bond formation over 20 years ago (Klopfer, 1971).

In non-primate mammals, there is evidence that OT induces the onset of maternal caregivingbehavior in hormonally primed females. Female rats (Pedersen, Caldwell, Walker, Ayers, & Mason,1994) and sheep (Da Costa, Guevara-Guzman, Ohkura, Goode, & Kendrick, 1996; Kendrick, Keverne,& Baldwin, 1987) can be induced to display maternal caregiving behavior by intracerebroventricularOT administration, while an injection of OT antagonist in rats shortly after parturition impairs the on-set of maternal caregiving behavior (Van Leengoed, Kerker, & Swanson, 1987). It has been suggestedthat variation in OT receptor density in various brain regions may underlie both species and individualdifferences in alloparental care in rodents (Olazábal & Young, 2006). Furthermore, while OT is notessential for maternal caregiving behavior to occur after its onset (Insel, 1997; Pedersen, 1997), theamount of pup licking and grooming in rats is positively affected by post-partum levels of OT (Cham-pagne, Diorio, Sharma, & Meaney, 2001; Francis, Champagne, & Meaney, 2000). Thus, OT induces theonset of maternal caregiving behavior in rats and sheep, and after its onset some forms of maternalcaregiving behavior may continue to be affected by OT levels.

In non-human primates, studies suggest that OT facilitates maternal caregiving behavior (Boccia,Goursaud, Bachevalier, & Pedersen, 2005; Holman & Goy, 1995). Recent preliminary findings by Boc-cia, Goursaud, Bachevalier, Anderson, and Pedersen (2007) indicate that administration of an OTantagonist reduced maternal behavior in a nulliparous female rhesus monkey, providing further sup-port for this notion. Pedersen (2004), however, suggests that in primates, maternal caregiving behav-ior is less determined by hormonal control, but instead is mainly acquired through early learning andsocial experience. This suggestion is in line with findings summarized in a review by Insel (2003) whoproposes a role for OT in linking external social signals to brain structures involved in motivation andreward, rather than activating maternal behavior. The maternal bond, therefore, may be the result ofthe motivation and rewards associated with carrying out maternal caregiving behavior, as was previ-ously suggested by Panksepp, Nelson, and Siviy (1994).

In further support of a role of motivational systems in the maternal bond, Bartels and Zeki (2004)found that the periaqueductal gray area is activated when human mothers are exposed to pictures oftheir own children, as opposed to pictures of adults or unfamiliar children. Interestingly, the periaqu-eductal gray area is rich in OT receptors (Jenkins, Ang, Hawthorn, Rossor, & Iversen, 1984), has beenassociated with opioid-stimulated maternal caregiving behavior in rat mothers (Miranda-Paiva, Ribe-iro-Barbosa, Canteras, & Felicio, 2003), and plays an important role in drug withdrawal and depen-dence (see Christie, Williams, Osborne, & Bellchambers, 1997 for a review). In further support,infant crying induces brain activity in the ventral tegmental area of mothers and the authors note that‘‘crying infants, [. . .], and cocaine induce some similarities in brain activity in regions where the dopa-minergic approach pathways are located” (Lorberbaum et al., 2002, p. 442). Taken together, these find-ings may indicate that the brain mechanism that promotes a proper response to infant stimuli sharesits neural substrate with brain addiction centers. It may therefore be that maternal caregiving behav-ior itself is rewarding, much like appetitive behaviors (see Spruijt, van den Bos, & Pijlman, 2001), andthat the maternal bond is a result of expressing maternal caregiving behavior toward the infant (assuggested by Panksepp et al., 1994).

Actual experimental research on the effects of OT on the maternal bond in humans is, because ofthe obvious ethical constraints, non-existent. Recently, however, an observational study by Levineet al. (2007) has shown that basal peripheral oxytocin concentrations in human mothers are relatedto both maternal behavior and maternal bond. They sampled peripheral oxytocin during pregnancyand the first month post-partum and found that oxytocin concentrations were fairly stable over time


and that they positively correlated with the quality of both maternal behavior and the maternal bondas reported in the Yale Inventory of Parent Thought and Action (YIPTA) questionnaire. Animal studieson the effects of OT on the maternal bond are rare, possibly due to the fact that rodent mothers displayno special preference for their own offspring but instead ‘bond’ with young pups in general (Pedersen,2004). However, pair bonding, which may be functionally similar to the maternal bond (Carter, 1998;Insel, 1997), has been studied extensively in the prairie vole, a rodent species that, in contrast with theclosely related montane vole, displays monogamous pair bonds. OT plays an essential role in the bondformation process, as central administration of OT to female prairie voles facilitates pair bonding whileOT antagonist administration impairs pair bonding (Insel & Hulihan, 1995). Moreover, the OT receptordistribution in female montane voles resembles that of prairie voles only when parental behavior ispresent (Insel, 1997; for a review: Wang & Aragona, 2004).

In sum, there is reasonable evidence that OT-mediated mechanisms may promote maternal care-giving (as a reflection of the maternal bond) through reward-related mechanisms.

ProlactinThe role of PRL in maternal caregiving behavior has been extensively reviewed (González-Mariscal

& Poindron, 2002; Mann & Bridges, 2001) and will only be briefly discussed. Studies show that admin-istration of PRL hastens the onset of maternal caregiving behavior in nulliparous, hormonally primedrats (Bridges, DiBiase, Loundes, & Doherty, 1985), while inhibiting PRL secretion or blocking PRL recep-tors delays it (Bridges, Numan, Ronsheim, Mann, & Lupini, 1990; Bridges, Rigero, Byrnes, Yang, &Walker, 2001). While steroid treatment alone will induce maternal caregiving behavior in rats, onlythe presence of PRL during steroid treatment will sustain some maternal caregiving behaviors until7 days post-partum (Orpen, Furman, Wong, & Fleming, 1987). Also, maternal PRL levels positively cor-relate with the amount of maternal caregiving behavior displayed by rat dams in response to ultra-sonic vocalizations of rat pups (Hashimoto, Saito, Furudate, & Takahashi, 2001), indicating that theimportance of PRL in rat maternal caregiving behavior extends beyond its onset.

The first study on the role of PRL in caregiving behavior in primates describes how carrying off-spring increases PRL levels in male marmosets (Dixson & George, 1982), but these findings do not indi-cate a direction of the effects. Similar effects have been found in male tamarins and marmosets(Roberts et al., 2001a; Schradin, Reeder, Mendoza, & Anzenberger, 2003), and female marmosets (Rob-erts et al., 2001a), female squirrel monkeys (Soltis, Wegner, & Newman, 2005), and female cotton-toptamarins (Ziegler & Snowdon, 2000). So far, the only study indicating a directing rather than corollaryrole of PRL on maternal caregiving behavior comes from Roberts et al. (2001b), who suggest thatblocking of PRL secretion inhibits infant retrieval in both male and female common marmosets. A re-cent study by Almond, Brown, and Keverne (2006), however, indicates that suppression of PRL doesnot affect paternal caregiving in experienced male common marmosets.

In human fathers, a positive correlation between PRL levels and couvade (male pregnancy) symp-toms has been found (Storey, Walsh, Quinton, & Wynne-Edwards, 2000). Experienced fathers show agreater increase in PRL than inexperienced fathers after they hear an infant cry, and fathers with high-er baseline PRL levels respond more alertly to infant hunger cries (Fleming, Corter, Stallings, & Steiner,2002). This suggests a functional directing mechanism through which PRL mediates paternal care, andthat caregiving experience may correlate with a greater prolactin-mediated sensitivity to infant stim-uli. However, while a correlation between PRL levels and paternal behavior has been found, little evi-dence exists for a similar mechanism in human mothers. This may be due to methodologicaldifficulties, because PRL levels in puerperal mothers may be caused by infant contact or post-partumendocrine processes. Because of the postulated homology between male and female neuroendocrinecircuitries (Wynne-Edwards, 2001), a role of PRL in the onset and maintenance of maternal caregivingbehavior is possible and further studies in, for instance, non-lactating mothers or young femalesshould be undertaken to determine whether this relationship exists in human mothers or femalesin general.

In sum, while a role of PRL in maternal caregiving is likely, this relation has not been investigated inhuman mothers. It is unclear whether PRL directly affects the maternal bond, but we note that thematernal caregiving that may be promoted by PRL may indirectly promote both the maternal bondand infant attachment.


Non-nutritive aspects of breastfeeding: Potential effects on infant attachment

In addition to the (endocrine) effects of breastfeeding that may promote maternal caregivingbehavior and bond formation, non-nutritive aspects of breastfeeding may promote infant attachment.Breastfeeding allows the mother to know what her infant is doing through direct sensory feedback,potentially promoting attachment through better attunement of mother–infant feeding interactions.

An important predictor of later infant–mother attachment is the mother’s sensitivity toward herinfant’s behaviors (De Wolff & Van IJzendoorn, 1997; Nievar & Becker, 2008; Van den Boom, 1994).Formation of a secure attachment is stimulated by a sensitive and consistent response to the infant’ssignals. While breastfeeding may offer the infant distinct visual, tactile and olfactory stimuli, it mayalso affect the mother’s behavior during feeding (Note: by the mother’s behavior, we do not meanmaternal caregiving behavior, but rather her general behavior), thus offering the suckling infant dif-ferent interactive experiences with the mother.

Direct feedback through nipple stimulation may promote mother–infant attunement during feed-ing interactions. Attunement, defined as the mutual adjustment of emotional and attentive states, canbe considered a key element of maternal sensitivity, and as such, attunement has been found to con-tribute to later attachment security (Feldman, 2007; Jaffe, Beebe, Feldstein, Crown, & Jasnow, 2001;Schore, 2000, 2001a, 2001b; Siegel, 2001). Correlations between interaction synchrony, defined asthe extent to which an interaction is reciprocal and mutually rewarding and therefore a measurableindex of attunement, and later attachment security were found when the mother–infant interactionwas observed at as early as one month of age (Isabella & Belsky, 1991; Isabella, Belsky, & von Eye,1989).

In addition to potentially fostering maternal sensitivity and mother–infant attunement, breastfeed-ing has been shown to positively affect maternal emotion (Mezzacappa, 2005, for a review). For exam-ple, breastfeeding increases maternal satisfaction (Kavanaugh, Meier, Zimmermann, & Mead, 1997),and it has also been suggested that breastfeeding might decrease negative mood, while bottle-feedingwould decrease positive mood (Mezzacappa & Katkin, 2002). Uvnäs-Moberg (1996) postulates thatbreastfeeding has a calming effect on mothers. This has been later supported by Heinrichs et al.(2001), who suggest that breastfeeding increased calmness as tested by a questionnaire. These dataare supported on a physiological level: mothers have a dampened stress response to both physicaland psychological stressors directly after breastfeeding (Altemus, Deuster, Galliven, Carter, & Gold,1995; Amico, Johnston, & Vagnucci, 1994; Heinrichs et al., 2001), an effect that may be mediated bythe hormonal response to breastfeeding (Heinrichs, Baumgartner, Kirschbaum, & Ehlert, 2003; Lightet al., 2000). Other experiments suggest that the pulsatile patterns of OT release that are characteristicof breastfeeding are associated with a desire to please and interact socially (Nissen, Gustavsson, Wid-strom, & Uvnas-Moberg, 1998; Uvnäs-Moberg, Widström, Werner, Matthiesen, & Winberg, 1990).Interestingly, the amount of milk given to the infant during breastfeeding also correlated with this de-sire for socialization (Uvnäs-Moberg, 1997). In sum, there is evidence that by breastfeeding, mothersmay become calmer and more sociable, which in turn may promote attachment security.

Empirical studies on breastfeeding and the mother–infant relationship

A literature search was carried out in PsychInfo, Medline, and the International Bibliography for theSocial Sciences for papers published after 1985 and written in English, combining the terms ‘‘bond*”and/or ‘‘attachment” with ‘‘breast?feed*”. The initial search yielded 328 papers, which, after readingthe abstract of each paper and eliminating duplicate results, was reduced to 41 papers mentioninga relation between breastfeeding and the maternal bond or attachment. Out of these 41 papers, 22 pa-pers make general statements on the positive effect of breastfeeding on either facet of the mother–in-fant relationship without a reference to empirical studies supporting this claim. In 13 papers, thereasons why parents choose to breastfeed their children are empirically examined. These papers gen-erally conclude that parents reported better bond formation through breastfeeding or that improvedbond formation was a reason for starting or extending breastfeeding. For example, Gijsbers et al.(2005) conclude that ‘‘The most important influencing factors regarding initiation and continuation


of breastfeeding were . . .bonding”. While these papers provide valuable information regarding paren-tal reasons for providing breastfeeding, they do not directly examine the relation between breastfeed-ing and the quality of the mother–child relationship.

Finally, six empirical studies directly examined the association between breastfeeding and eitherthe maternal bond or infant attachment. These studies are summarized in Table 1 and will be dis-cussed in the following paragraphs.

As shown in the table, three studies related breastfeeding to the maternal bond. In the study byCernadas et al. (2003), the quality of the mother–infant bond was rated by three experienced observ-ers during the first days after birth. A better bond was significantly correlated with a longer duration ofexclusive breastfeeding, as assessed by monthly telephone interviews during the first 6 months of life.The correlation should be interpreted with caution, however, because the study was set up to examinethe effect of the maternal bond on breastfeeding, and not the effect of breastfeeding on the maternalbond. However, these findings do indicate that studies on the relation between the occurrence ofbreastfeeding and the quality of the mother–infant relationship need to take into account the reci-procity of the relationship; breastfeeding may promote the maternal bond, but mothers who bondbetter with their infants may also be more likely to choose to breastfeed over bottle-feeding.

In a study in mothers who exclusively breastfed or bottle-fed from birth, Martone and Nash (1988)found no relation between feeding method and maternal affective behavior during a feeding interac-tion at two days post-partum. Using the Avant maternal–infant attachment tool, Martone and Nashobserved 15 breastfeeding and 15 bottle-feeding mother–infant pairs during a feeding session inthe hospital. Their choice for observing at 2 days post-partum may have been motivated by the ongo-ing debate on a critical bonding period, and, unfortunately, the maternal bond was not assessed at la-ter ages. If breastfeeding does affect bond formation, differences are to be expected after some time.Thus, while neonatal measures of the maternal bond are important for providing a ‘basal’ score, effectsof breastfeeding on the maternal bond can only be determined through later assessments.

The third study relating breastfeeding to the maternal bond was performed by Else-Quest et al.(2003) who reported a weak and non-significant relationship between breastfeeding and the maternalbond. In their longitudinal study, breastfeeding and bottle-feeding mothers filled in the ParentingStress Index at 4 and 12 months post-partum, which includes a scale on maternal attachment. At4 months post-partum, breastfeeding mothers showed a non-significant tendency to score lower onthe maternal attachment scale than bottle-feeding mothers, indicating a better bond. When retestedat 12 months, no differences between breast- and bottle-feeding mothers were found. The reverse wasfound with regard to the quality of the parent–child interaction, which was videotaped at home at 4and 12 months and rated using the Parent–Child Early Relational Assessment (PCERA; Clarke, 1985).While breastfeeding mothers did not differ from bottle-feeding mothers at 4 months, some differenceswere found at 12 months. Bottle-feeding mothers showed significantly more negative affect and be-haved more intrusively than breastfeeding mothers, and their infants displayed more dysregulationand irritability as compared to the infants of breastfeeding mothers. Else-Quest et al. further elaborateon their findings stating that although there were differences between breast- and bottle-feeders, bot-tle-feeding mothers scored well within the range of scores corresponding to good-quality relation-ships on the PCERA.

As shown in Table 1, three empirical studies have investigated the relation between breastfeedingand children’s attachment. In the earliest study, Fergusson and Woodward (1999) examined the asso-ciation between breastfeeding and the parent–child relationship in a large cohort of children(N = 999). From birth to 1 year of age, information was collected on maternal breastfeeding practices,and at 15–18 years of age the children themselves filled out the Inventory of Parent and Peer Attach-ment (IPPA), a questionnaire that is designed to measure the quality of children’s attachment to theirmother, father, and peers (separate scores). In Fergusson and Woodward’s study, the scores for attach-ment to mother and father were combined into one overall score for the quality of attachment to bothparents. The children were classified into four groups: no breastfeeding (29.6% of the sample),<4 months (27.1%), 4–7 months (19.4%), and >7 months (23.8%). Fergusson and Woodward report thatbreastfeeding duration was significantly associated with higher quality attachment to parents, butafter adjusting for confounders, the effect of breastfeeding duration disappeared. It should be notedthat some important methodological constraints may have compromised the outcome of this study.

Table 1Overview of studies on breastfeeding and the mother–infant relationship

Authors Bonding/attachment

Assessmentinstrument

Infant age atassessment ofBonding/attachment

N Breastfeedingmeasures

Confoundingdemographicmeasures

Results

Cernadas et al.(2003)

Bonding Observation (Self-designed)

<3 days 529 Initiation,Duration

Age, Parity,Education*

A longer duration of exclusive breastfeeding was associated withgood mother–infant bonding

Else-Quest et al.(2003)

Bonding Maternal report(Questionnaire, PSI)

4 months, 12 months 570 Initiation Age, SES,Education*

Non-significant tendency of breastfeeders to report experiencingbetter bonding with their infant at 4 months. No differences at12 months

Martone andNash (1988)

Bonding Observation(AVANT)

2 days 30 Initiation None reported No significant differences between breast- and bottle-feedingmothers

Britton et al.(2006)

Attachment Observation (SSP) 12 months 152 Initiation,Duration

Age*, SES*,Education*,Ethnicity*

No relationship between breastfeeding and attachment security

Gribble (2006) Attachment Maternal report(Unstructuredinterview)

Varying (6 months to5 years)

4 Initiation None reported Although not statistically tested, a role of breastfeeding inpromoting infant attachment is suggested

Fergusson andWoodward(1999)

Attachment Child report(Questionnaire,IPPA)

15–18 years 999 Initiation,Duration

Age*, Parity*,SES*, Education*

After adjustment for demographic factors, breastfeeding was notrelated to perceived attachment to parents

Confounding Demographic Factors noted with * were significantly different between breast- and bottle-feeding populations. When significantly different, breastfeeding populations wereolder, multiparous, had higher education levels and SES, and were not part of an ethnic minority. In all studies, significantly different confounders were always controlled for.

512J.Jansen

etal./D

evelopmental

Review

28(2008)

503–521


By measuring attachment only when the children were 15–18 years of age, a possible transient effectof breastfeeding on attachment could not be detected. Furthermore, effects of other potential determi-nants of attachment, such as non-feeding-related mother–child interactions and significant life eventsin the intervening period, were not controlled for. And finally, while breastfeeding is an interactionbetween the mother and her infant, the child’s attachment to both parents was taken as an outcomemeasure in this study.

Gribble (2006), in a review on breastfeeding and attachment, presents four case studies in whichbreastfeeding promoted attachment in adopted infants. However, while these cases are intriguing,we are of the opinion that this study does not provide sufficient evidence of a role of breastfeedingin infant attachment. The four presented case studies all involve abused or neglected infants, andthe quality of the attachment relationship was not determined using the SSP or AQS, but was basedon maternal report. Finally, no cases of comparable, but non-breastfed, infants were presented, andthus the relative effect of breastfeeding is difficult to estimate, especially because adopting motherswho decide to breastfeed are likely to differ from the average population in other respects that maypromote infant attachment.

The third and final study relating breastfeeding to infant attachment is reported by Britton, Britton,and Gronwaldt (2006). This study was the first to examine breastfeeding in relation to infant attach-ment security as assessed with the Strange Situation Procedure. Britton et al. assessed breastfeedingintent (prenatally), and breastfeeding practice (initiation and duration) up to 12 months post-partum.Maternal sensitivity toward the infant during feeding was rated from videotape at 3 months and thequality of the mother–infant interaction was also rated at 6 months. Finally, the mother–infant dyads(n = 152) were observed in the Strange Situation. The results indicate that both breastfeeding intentand breastfeeding practice were positively correlated with maternal sensitivity at 3 months post-par-tum. However, Britton et al. did not find a relationship between breastfeeding practice and infantattachment: securely and insecurely attached dyads did not differ in breastfeeding initiation or dura-tion. While the results of this study do not completely eliminate the possibility that breastfeeding hasan effect on infant attachment, they do strongly indicate that if breastfeeding affects infant attach-ment, it will be a small effect at most.

Summarizing, there are few studies on the relation between feeding method and the maternalbond or infant attachment, and the findings of the studies that do explore a potential relation areinconclusive at most. It is, however, noteworthy that both Else-Quest et al. (2003) and Britton etal. (2006) find that breastfeeding is associated with differences in the quality of the interactionbetween mother and infant, with breastfeeding mothers doing better in both studies. The factthat no conclusive relation between feeding method and the mother–infant relationship has beenfound may indicate that breastfeeding is of little importance to the mother–infant relationship.However, given the importance of infant attachment for future development, and the conse-quences of poor maternal care for infant well being and development, we feel that it is war-ranted to discuss whether the absence of empirical support for a role of breastfeeding in themother–infant relationship indicates that no such relationship exists, or whether it may be theresult of methodological issues, because theoretical grounds on which an effect of breastfeedingon the maternal bond or infant attachment exist. The following section therefore discusses gen-eral methodological constraints that may have hindered previous studies, at the same time offer-ing possible solutions for future studies.

General methodological constraints

As previously shown, there are theoretical mechanisms through which breastfeeding may promotethe maternal bond or attachment. However, scientific support of this assumption is scarce. Again, thiscould indicate that breastfeeding does not affect the maternal bond or infant attachment, but may alsobe the result of the general lack of empirical studies on the subject and of methodological problems ofthese studies. In this section, we will further discuss general methodological issues concerning re-search on breastfeeding practice, the maternal bond, and infant attachment that may provide an alter-native explanation for the lacking relationship.


Breastfeeding

Modern human breastfeeding practice has changed to such an extent that the validity of animalresearch data that supports a possible role of breastfeeding in promoting the mother–infant relation-ship is uncertain. We argue that in order to assess the importance of breastfeeding for the mother–in-fant relationship, studies should carefully report the specifics of breastfeeding behavior, such asoverall duration and number of feeds per day, in order to better specify which factors do or do notexert any effect. To this end, we will shortly discuss studies explaining why these factors are ofrelevance.

The importance of taking breastfeeding duration into account becomes apparent when comparinghuman and non-human primate nursing duration. Primate studies show that the young are weanedwhen their birth weight has tripled (in humans after approximately 3 years) or after they reach aboutsix times their gestation length (in humans after 4.5 years, Dettwyler, 1995; Dettwyler, 2004). How-ever, while the World Health Organization encourages exclusive breastfeeding for the first 6 monthspost-partum and continuation of breastfeeding until 2 years of age, there is evidence that in westernsociety breastfeeding duration can be even shorter. For example, current US data indicate that while70% of mothers start breastfeeding, only 33% continue to do so until the child is 6 months of age. Bear-ing in mind the developmental window of infant attachment, which only starts to become person-spe-cific after approximately 3 months and is still in full development during the second 6 months afterbirth, this may be very relevant. Therefore, it is possible that no effects on infant attachment are tobe expected when breastfeeding durations are very short.

Another factor that should be taken into account is the number of daily feeds, as an indication ofwhether infants are fed on-demand or at scheduled intervals. Ben Shaul (as cited in Blurton Jones,1972) notes that the composition of human milk, i.e., low protein and fat content, is indicative of acontinuous, on-demand, feeding schedule, as is seen in a multitude of tribal cultures. According to Fil-des (1986), breastfeeding frequency in Europe mostly followed the infant’s needs until approximately1750 AD, when English society women started scheduling their feeding regime in order to combinemotherhood and social responsibilities. The practice of scheduling feeds has continued in western civ-ilization in order to accommodate working mothers, although on-demand feeding is gaining popular-ity in certain groups. The number of daily feedings may be particularly important when investigatingthe effects of breastfeeding on the maternal bond, because the hormones that in theory may be ben-eficial are affected by both feeding behavior and frequency. OT concentrations may be sufficiently ele-vated to affect the maternal bond only in mothers who feed frequently. Supporting this suggestion,basal OT levels were found not to differ between breastfeeding and non-breastfeeding mothers (Le-vine et al., 2007; van der Post et al., 1997).

Thus, modern human breastfeeding behavior may not affect the mother–infant relationship, sincein western society we do not feed often enough to affect the maternal bond and not long enough toaffect infant attachment. This means that before any conclusions can be reached on whether breast-feeding does or does not affect the mother–infant relationship, it will be necessary to carry out studieson sufficiently large (non-western) populations, taking both breastfeeding duration and frequencyinto account.

Additionally, careful consideration should be given to moderating and mediating factors. In con-trast with non-western societies, in western society the decision to breastfeed has become a politicalissue that is affected by cultural perceptions, feelings of sexuality and integration, and conflict be-tween being a mother and pursuing a career (some of these themes have been reviewed by Van Ester-ik, 2002), and thus decisions on infant feeding are likely to differ between social groups. Not allmothers choose to breastfeed their babies. Mothers who initiate breastfeeding differ from bottle-feed-ing mothers in age, socio-economic status, ethnicity, smoking status, maternal employment and atti-tudinal and intrapersonal characteristics (Dennis, 2002). Women least likely to breastfeed areyounger, have a lower income and are likely to be from an ethnic minority. Furthermore, mothersdeciding to bottle-feed do so most often because of mother-centered reasons, whereas breastfeedingmothers do so for baby-centered reasons (Arora et al., 2000; Wiesenfeld, Malatesta, Whitman, Gran-rose, & Uili, 1985), suggesting pre-feeding differences in maternal motivation. These moderators maymask potential effects of breastfeeding (Corter & Fleming, 2002), and, as can be seen in Table 1, may


compromise the validity of the results. Thus, studies should always compare breast- and bottle-feed-ing mothers controlling for maternal age, parity, education level, ethnicity (in multi-ethnic researchpopulations), socio-economic status, and other possible confounders such as the presence or absenceof other children.

As discussed before, an effect of breastfeeding on the mother–infant relationship need not be a di-rect effect, but may be mediated by other factors. Although they find no evidence in their sample, Brit-ton et al. (2006) suggest that an effect of breastfeeding on infant attachment may be mediated byalterations in maternal sensitivity. Likewise, maternal mood may affect any mother–infant interactionand may thus have an effect on later infant attachment or the maternal bond. Accounting for thesepotential mediators of later attachment security may be beneficial for detecting a potential effect ofbreastfeeding on the mother–infant relationship.

The maternal bond

Research on the maternal bond suffers from a number of problems. First, the maternal bond hasbeen poorly defined, and as a result, current research suffers from the negative associations withthe bonding research that was carried out nearly 25 years ago. We propose to define the maternalbond as the tie from mother to infant that promotes maternal behaviors aimed at mother–infant prox-imity and caregiving.

Second, because the developmental course of the maternal bond is unclear, its development, or lackthereof, should be assessed throughout the infant’s first years of life, preferably even starting duringpregnancy, and with repeated measurements during the first year.

Finally, there has been no evaluation of instruments to assess the maternal bond. It has been mea-sured by self-report questionnaires (Parental Stress Index in Else-Quest et al., 2003; Post-partumBonding Questionnaire in Edhborg, Matthiesen, Lundh, & Widström, 2005; Maternal AttachmentInventory in Müller, 1994; Yale Inventory of Parental Thoughts and Action in Feldman et al., 1999)and with behavioral observations coded with qualitative rating scales (self-designed in Cernadas etal., 2003; Avant-tool in Martone & Nash, 1988). All these instruments are likely to assess different as-pects of the maternal bond. As an example, questionnaires that have been developed for use in a clin-ical setting, such as the bonding scale of the Parental Stress Index (PSI: Abidin, 1986) or the Post-partum Bonding Instrument (PBI: Brockington et al., 2001), are designed toward diagnosing potentialfailure in maternal bond formation, but are unable to quantify the maternal bond beyond its presenceor (if possible) absence. Likewise, the self-designed observational scale used by Cernadas et al. (2003)distinguishes between a ‘very good’, ‘good’, and ‘fair’ bond, based on the amount of baby-directedtouching, holding and looking of the mother. The discriminating power of this scale appears to below, however, as only 14 out of 529 mothers were characterized as bonded ‘fair’, the others falling intothe ‘very good’ (n = 223) or ‘good’ (n = 302) category. Therefore, for any potential effect of breastfeed-ing on the maternal bond to be investigated, current methods should be compared and refined.

We also recommend the development of new research tools for assessing the maternal bond. Whilethese new tools could be questionnaires, this area of research would greatly benefit from alternativemethods to assess the maternal bond. Questionnaires often suffer from social desirability of the an-swers, and outcomes are likely to be confounded by maternal mood or psychopathology (Hornsteinet al., 2006; Moehler, Brunner, Wiebel, Reck, & Resch, 2006). It should be noted, however, that whenmeasuring the maternal bond through observation, various but specific components of the maternalbond should be invoked (e.g., ‘motherese’ vocalizations, maternal gaze, and touch; Levine et al.,2007), in an interaction comprised of various situations (e.g., infant present and absent, during freeplay and a structured task). In their study on breastfeeding and the maternal bond, Martone and Nash(1988) observed mother–infant pairs only during feeding and thus any difference in maternal caregiv-ing behavior may reflect behavioral differences inherent to the situation, rather than differences in thematernal bond. One of the future goals of research on the maternal bond therefore will be to carefullytheorize on various components of the maternal bond and how these may be measured, and to there-after test these theories using standardized situations or procedures.

Experimental paradigms that assess subconscious associations, such as the startle response proce-dure (Spangler, Emlinger, Meinhardt, & Hamm, 2001) or the implicit association test (IAT: Greenwald,


McGhee, & Schwartz, 1998), could be ideally suited to quantify the motivational and emotional as-pects of the maternal bond, because they circumvent issues such as social desirability or situation spe-cific differences during observations. Standardized mother–infant interactions, much like the strangesituation procedure for measuring infant attachment, may allow measurement of quality and quantityof specific maternal behaviors.

Infant attachment

Whereas research on the maternal bond is hampered by a plethora of research tools that mostlylack applicability beyond a clinical setting, the Strange Situation Procedure and the Attachment Q-Sorthave been widely accepted as the gold standards of attachment security assessment in a wide area ofinfant research.

However, the use of the widely applied ‘‘secure” versus ‘‘insecure” dichotomization that resultsfrom the Strange Situation Procedure may not be best for assessing infant attachment in studies wheresmall effects are expected (such as when determining the effect of breastfeeding on infant attach-ment). Although these categorical scores have been successfully applied in numerous studies (e.g.,predicting attachment from parental sensitivity, or predicting future development from attachment),the sensitivity of dichotomized scores is constrained because differences in attachment security be-tween infants within categories are not taken into account; that is to say, infants classified as ‘‘secure”are all treated as equally secure. It is possible that the AQS, which yields continuous security scores, ismore suitable for detecting (subtle) influences of breastfeeding on attachment security (see also Fraleyand Spieker (2003) for further discussion on the use of a continuous versus categorical attachmentscore).

Furthermore, both the SSP and the AQS are aimed at assessing attachment security after a clear-cutattachment has been formed, and are therefore not applicable for assessing the quality of the devel-oping attachment relationship during the first year of life. One could argue that attachment securityis ‘in the making’ during the first year, and that the validity of early measures may be low, but studiescorrelating early infant visual attention with later attachment security (Grossman, Grossman, Span-gler, Suess, & Unzner, 1985; Koulomzin et al., 2002) indicate that there are key behaviors that maypredict later attachment. Measures to assess ‘attachment-in-the-making’ in the first year of life mightbe very useful in studying the effect of breastfeeding on the developing infant–mother attachmentrelationship. An interesting candidate might be the Induced Stress at Home (ISH) procedure, devel-oped by Hoeksma, Koomen, and Van den Boom (1996). Hoeksma et al. used the ISH procedure to lon-gitudinally study the development of the attachment behavioral system in a group of infants between3 and 12 months of age. Approximately one week after the last ISH procedure, the infants and theirmothers were also subjected to the Strange Situation Procedure. The ISH was shown to be a valid mea-sure to induce and measure the attachment behaviors proximity seeking, contact maintaining, andavoidance. The ISH procedure might therefore be an interesting procedure for studies examiningthe effects of breastfeeding on infant–mother attachment.

Conclusion

The scientific research carried out to date does not support the general assumption that breastfeed-ing has a positive effect on the quality of the mother–child relationship. When propagated, such anassumption may create unnecessary feelings of guilt in mothers unable to breastfeed. Recommenda-tion of breastfeeding should therefore solely be based on its well-documented positive effects on in-fant and maternal health.

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