AOGS MAIN RESEARCH ARTICLE

Anthropometric measurements as predictors ofcephalopelvic disproportionSANTOSH J. BENJAMIN1, ANJALI B. DANIEL2, ASHA KAMATH2 & VANI RAMKUMAR3

1Department of Obstetrics and Gynaecology, Christian Medical College, Vellore, Tamilnadu, India, 2Department ofCommunity Medicine and 3Department of Obstetrics and Gynaecology, Kasturba Medical College, Manipal, Karnataka, India

Key wordsAnthropometric measurements, cephalopelvicdisproportion, fetal weight estimates

CorrespondenceDr. Santosh Benjamin, Department ofObstetrics & Gynaecology, Christian MedicalCollege, Vellore 632004, Tamilnadu,India.E-mail: toffeetripper@gmail.com

Conflict of interestThe authors have stated explicitly that thereare no conflicts of interest in connection withthis article.

Please cite this article as: Benjamin SJ, DanielAB, Kamath A, Ramkumar V. Anthropometricmeasurements as predictors of cephalopelvicdisproportion. Acta Obstet Gynecol Scand2012; 91:122127.

Received: 15 October 2010Accepted: 28 August 2011

DOI: 10.1111/j.1600-0412.2011.01267.x

Abstract

Objective. We assessed the efficacy of maternal anthropometric measurements andclinical estimates of fetal weight in isolation and in combination as predictorsof cephalopelvic disproportion (CPD). Design. Prospective cohort study. Setting.Tertiary care teaching hospital, two affiliated hospitals with facilities for conduct-ing cesarean delivery and seven affiliated primary care facilities with no operationtheaters. Sample. Primigravidae over 37 weeks gestation attending these facili-ties during a 20-month period with a singleton pregnancy in vertex presentation.Methods. Several anthropometric measurements were taken in 249 primigravidae.Fetal weight was estimated. Differences in these measurements between the vaginaldelivery and CPD groups were analyzed. The validity of these measurements inpredicting CPD was analyzed by plotting receiver operating characteristic curvesand by logistic regression analysis.Main outcomemeasure.Mode of delivery.Results.Maternal height, foot size, inter-trochanteric diameter and bis-acromial diametershowed the highest positive predictive values for CPD. Combining some maternalmeasurements with estimates of fetal weight increased predictive values modestly,which are likely to be greater if the estimates of fetal weight are close to the ac-tual birth weight. Based on multivariate analysis the risk factors for CPD in ourpopulation were foot length 23cm, inter-trochanteric diameter 30cm and esti-mated fetal weight 3 000g. Conclusions. Maternal anthropometric measurementscan predict CPD to some extent. Combining maternal measurements with clinicalestimates of fetal weight only enhances the predictive value to a relatively modestdegree (positive predictive value 24%).

Abbreviations: CPD, cephalopelvic disproportion; ROC, receiver operating charac-teristic; PPV, positive predictive value.

Introduction

Maternal deaths remain amajor problem in some developingregions of the world such as sub-Saharan Africa and southAsia (1,2). Cephalopelvic disproportion (CPD) is in suchcircumstances an important cause of maternal and perinatalmortality and is also associated with considerable morbidityfor both the mother and the baby (14). Perineal tears, post-partum hemorrhage, and obstetric fistulae in the mother,and birth asphyxia and birth trauma in the newborn are allassociated with CPD (46).

Timed optimally, a cesarean delivery for CPD is best for themother aswell as her fetus; to facilitate this it is imperative that

CPD is diagnosed sufficiently early. The consequences of latedetection areparticularly grave in thedevelopingworldwherethe mother may go into labor in a setting where facilitiesfor performing cesarean section are inadequate (6). In suchsituations, it is vital that women at potential risk of CPD areidentified prior to the onset of labor to facilitate referral to acenter where a cesarean delivery can be performed.

Measurement of maternal height has been used as a simplemeans to identify women at risk of CPD, as it is assumedthat the shorter the mother, the greater the likelihood ofCPD (710). However, maternal height in isolation has lim-ited value for predicting CPD risk (11) and combining an-thropometric measurements may increase the likelihood of

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S. J. Benjamin et al. Anthropometric predictors of CPD

predicting CPD (12). Since anthropometry and stature ofwomen of different ethnic origins vary, it is important toidentify the most sensitive predictors of CPD for a particularpopulation.

We assessed the efficacy of using maternal height, footsize and other anthropometric measurements as predictorsof CPD in a cohort of women from southwest India andincluded estimated fetal weight as an additional predictor.

Material and methods

This prospective cohort studywas carriedout at a tertiary careteaching hospital (KasturbaHospital), two affiliated hospitalswith facilities for conducting cesarean delivery, and sevenaffiliated primary care facilities with no operation theaters.

Primigravidae of >37 weeks gestation who attended anyof these facilities over a 20-month period with a singletonpregnancy in vertex presentation were eligible for inclusionin the study.

The women were recruited on each day from the centerwhere the principal investigator (S.J.B.)was onduty; the sam-ple accounts for approximately 15% of the women deliveringat these facilities.

The height, bis-acromial, inter-cristal, inter-trochantericdiameters, foot length, vertical and transverse diameters ofthe Michaelis rhomboid, symphysio-fundal height and ab-dominal girth were measured for each woman (Figure 1).

Height was recorded on a stadiometer with an accuracyof 0.5cm; a modified Harpenden anthropometer with an

Figure 1. Various anthropometric measurements made in the study.The transverse diameter of the Michaelis sacral rhomboid was measuredbetween the two posterior superior iliac spines. The vertical diameter ofthe rhomboid was measured between the L5 spine (one space belowthe L3L4 disc which is in line with the uppermost point of the iliac crest)and the upper limit of the natal cleft.

accuracy of 0.1cm and a tape measure were used for othermeasurements. With the patient lying supine with kneesflexed, fundal height was marked after correcting uterinedextro-rotation. Then, with the patients knees straight-ened, the distance from the symphysis to the point marked(symphysio-fundal height) was noted (13). The abdominalgirth was measured with a measuring tape at the level of theumbilicus.

Fetal weight was estimated both as the product of thesymphysio-fundal height (cm) and the abdominal girth (cm)and expressed in grams (1315) and using Johnsons formula(16) which is calculated from the symphysio-fundal heightin centimeters a constant according to level of fetal headengagement 155. Mode of delivery was recorded as normalvaginal, instrumental vaginal (forceps, vacuum extraction),cesarean delivery for CPD or cesarean delivery for other in-dications. The former was defined as emergency cesareandelivery performed for failure of descent of the fetal heador failure of progress following a trial of labor, where therewas no change in the cervical dilation for 4 hours in theactive phase of labor following rupture of the membranesdespite adequate uterine contractions (three contractions/10minutes, each >45 seconds) in the presence of a well flexedhead. Fourteen patients who were short and considered tohave a large fetus had elective cesarean delivery and wereexcluded from analysis.

Intra-observer reproducibility alone was evaluated (onlyone investigator). Forty women had all anthropometricmea-surements repeated on two separate occasions without theinvestigator having access to the values of the first measure-ment session.

Statistical analysis

The Statistical Package for Social Sciences (SPSS version 15.0for Windows) was used. Reproducibility was estimated bycomputing the coefficient of variation. The sensitivity andspecificity of each anthropometric measurement was com-puted and receiver operating characteristic (ROC) curvesplotted. Stepwise logistic regression was used to identify pre-dictors of CPD. The optimal cut-off for each variable wasobtained using the ROC analysis. To obtain predicted prob-abilities, all the variables with the optimal cut-off that weresignificant at the 0.2 level in the univariate analysis were in-cluded for the logistic regression.

For analysis, normal vaginal and instrumental deliverieswere grouped together as a single outcomemeasure for com-parison with the CPD group. Analysis of variance followedby post-hoc Tukeys test was used to compare differencesbetween the vaginal delivery and CPD groups. Spearmanscorrelation coefficients were computed to compare the esti-mates of fetal weight with actual birth weight. A p-value of

Anthropometric predictors of CPD S. J. Benjamin et al.

Table 1. Comparison of maternal anthropometric characteristics and fetal weight between three modes of delivery.

Vaginal delivery Cesarean delivery for CPD Cesarean delivery for(n=172) (n=27) other indications (n=50) p-value

Maternal age (years) 24.93.4 26.03.3 25.74.0 0.188Height (cm) 157.16.6 152.16.0 154.65.0

S. J. Benjamin et al. Anthropometric predictors of CPD

Table 3. Validity of combining different maternal anthropometric mea-

surements and fetal weight for prediction of CPD

Sensitivity Specificity PPVpercentage percentage percentage

Height+foot length 63.4 61.7 16.7Height+estimated

fetal weight(Johnsons formula)

81.5 60.4 20.0

Height+estimatedfetal weight(clinical)

81.5 61.7 20.6

Footlength+estimatedfetal weight(Johnsons formula)

74.1 68.5 22.2

Footlength+estimatedfetal weight(clinical)

74.1 68.5 22.2

Height+ footlength+estimatedfetal weight(Johnsons formula)

70.4 56.8 16.5

Height+ footlength+estimatedfetal weight(clinical)

70.4 73.0 24.1

PPV, positive predictive value.

diameters did not increase the predictive value appreciably(data not shown in Table 3). If the estimate of fetal weight wasequal to the true birthweight and combined with maternalheight and foot length, the positive predictive value rose to34.9. Multivariate logistic regression analysis identified threesignificant predictors of CPD; inter-trochanteric diameter30cm (OR: 2.8; 95%CI: 1.2,6.9), foot length 23cm (OR:4.0; 95%CI: 1.5,10.7) and clinically estimated fetal weight3 000g (OR: 3.4; 95%CI: 1.3,9.3). The predicted proba-bility for CPD if all three measurements were outside thesethresholds was 32.3%. There was a positive correlation be-tween the estimates of fetal weight and actual birthweight(Spearmans rank correlation coefficient =0.60, p

Anthropometric predictors of CPD S. J. Benjamin et al.

Table 4. Maternal anthropometric characteristics and fetal weight in normal vaginal deliveries, instrumental vaginal deliveries and cesarean deliveries

for CPD.

Normal vaginal delivery, Instrumental vaginal delivery, Cesarean delivery for CPD,Variables (cm) n=146 n=26 n=27 p

Height 157.06.9 157.34.9 152.16.0

S. J. Benjamin et al. Anthropometric predictors of CPD

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