low intelligence andobstetric complications* · direct contribution of recognized obstetric...

Brit. J. prev. soc. Med. (1966), 20, 15-21

LOW INTELLIGENCE AND OBSTETRIC COMPLICATIONS*

BY

D. J. P. BARKERDepartment of Social Medicine, University ofBirnmngham

Investigations into the association between lowintelligence and obstetric complications have beeninconclusive. Dayton (1930) wrote that "the litera-ture on mental deficiency is replete in its referencesto difficult labour as an aetiological factor in theproduction of intelligence defects". But in a retro-spective inquiry he found no evidence that abnormaldeliveries were associated more frequently with thebirths of subnormal children. Pasamanick andLilienfeld (1955) looked at the birth records of sub-normal children in Baltimore and concluded that"the pre-natal and paranatal records of mentallydefective children born in Baltimore between 1935and 1952 showed significantly more complications ofpregnancy and delivery, prematurity, and abnormalneonatal conditions than a similar number ofmatched controls. The non-mechanical abnor-malities such as bleeding during pregnancy andtoxaemia appear to be important factors in thisassociation rather than the mechanical factors ofdelivery previously described". Stott (1957) claimedthat "'pregnancy troubles might be responsible for alarge, and probably the greater part of the re-tardation" of the subnormal children whom he wasstudying. Rauramo, Gronross, and Kivikoski (1961)obtained the delivery reports of pupils in a schoolfor backward children, and concluded that there wasa raised incidence of forceps delivery, breech birth,toxaemia of pregnancy, and prolonged labour.

It is difficult to assess the results of these studiesbecause they are based on comparisons betweenunrepresentative samples of subnormal children andcontrol groups which do not seem adequate. Thesemethodological difficulties were largely overcome by

This work has been supported by grants from the Association forthe Aid of Crippled Children and from the Medical Research Council.

Fairweather and Illsley (1960). They identified themajority of subnormal children born in Aberdeenduring a single year and compared their birthhistories with those of the entire population born inthe city in the same year. They concluded that "thedirect contribution of recognized obstetric compli-cations to the total volume of mental handicap issmall". But, although they showed that the impor-tance of obstetric complications had been exag-gerated, they studied only 66 subnormal childrenand were unable to identify particular complica-tions associated with subnormality.The findings described below are based on a study

of 607 subnormal children for whose low intelligencethere is no known cause. These children were drawnfrom a population of 73,687 single births for whomobstetric data were recorded at the time of birth.

METHODSPOPULATION OF CHILDRENThe population comprised all children born in

Birmingham during the years 19504 (multiplebirths excluded) who lived in the City until the age of5 years. Obstetric data have been recorded for allbirths in Birmingham since 1950 and health visitorshave recorded the subsequent medical histories of thechildren (Charles, 1951).

There were 94,476 total births during the 5-yearperiod, from which the following were excluded:

(1) Stillbirths;(2) Deaths under 5 years of age;(3) Children untraced by health visitors one year

after birth;(4) Children known to have left the City between

the age of 1 and 5 years;(5) Twins and triplets.

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D. J. P. BARKER

There remained a population of 73,687 childrenwho were still in Birmingham when they reachedschool age (5 years).

ASCERTAINMENT OF CHILDREN OF LOW INTELLIGENCEThe following procedure was used to identify

children whose performance on intelligence testswas subnormal.

"Intellectual subnormality" was defined as anIntelligence Quotient (IQ) of less than 75 (using theTerman-Merrill revision of the Stanford-BinetIntelligence Scale Forms L and L-M). At the time ofthe survey the children studied were aged from 9 to14 years and the intellectually subnormal weretherefore in one of three educational categories:

(1) Those unsuitable for education (in the care ofthe Public Health Department with the majorityliving at home).

(2) The educationally subnormal (ESN) (usuallyattending special schools for the educationally sub-normal but occasionally in special schools forchildren with physical handicaps such as cerebralpalsy or epilepsy).

(3) Those on the borderline of subnormality (theleast accomplished children in primary or secondaryschools).

It was not possible to identify children in the lastcategory and the sources of ascertainment weretherefore restricted to the Public Health Departmentand the Special Schools Section of the EducationDepartment.The records in these departments permitted

identification of 753 intellectually subnormal childrenfrom the population. 237 of these children had beenclassed as unsuitable for education, and 516 wereattending special schools. Together they representedI 0 per cent. of the population, a lower incidencethan would be expected from the results of someother surveys (Penrose, 1963).There seem to be three ways in which ascertain-

ment of subnormal children may have been in-complete. First, it was not possible to identifyborderline subnormal children and this has un-doubtedly resulted in a deficiency at the higher levelsof subnormal intelligence. But inquiries have shownthat it is exceptional for a Birmingham child with anIQ of less than 65 to go through primary schoolunascertained, and the deficiency is probably confinedto the IQ range 65 to 74. At this level children whoare ascertained probably differ from those who arenot. For example, teachers may refer unintelligentboys for special schooling more readily than theyrefer unintelligent girls, and dull children with

physical deformities or disorders of temperamentwill be singled out sooner than others.A second cause of incomplete ascertainment

results from the lapse of time between the entry of asubnormal child into a primary school and thereferral of the child to an ascertaining clinic. Sincethe survey's population is composed of children whoentered schools m Birmingham at the age of 5 years,but are not known to have remained there sub-sequently, it is probable that some subnormalchildren left the city after reaching school age andbefore ascertainment as ESN or unsuitable foreducation. It is difficult to obtain precise informationabout the number of such children, but it is probablysmall. Although ascertainment ofsubnormal childrenwas spread over the entire primary school period, itwas maximal between 5 and 8 years and declinedsharply thereafter, so that the average age ofascertainment ofESN children was 7j years and thatof children unsuitable for education was 6 years.Over 75 per cent. of all subnormal children wereascertained before the age of 9 years. There are nodata to show the rate at which Birmingham-bornchildren move from the city while they are attendingprimary schools, but information about the emi-gration rate of pre-school children shows that thereis a decline with increasing age, and less than 2 percent. of those born in 1950-4 left the city when theywere 4 years old. It seems reasonable to assume that,with the entry of children into primary schools,families become less mobile; and it is unlikely thatthere are more than 35 subnormal children whoshould have been included in the study but left thecity before ascertainment.A third possible cause of defective ascertainnment

is the care of subnormal children in private insti-tutions without the knowledge of the local authority.There are three reasons for thinking that the numberof children cared for in this way is very small:

(1) The City's School Attendance and Bye-LawsDepartment makes an unusually thorough annualcensus of all children in the city, and since thepopulation which is being studied comprises childrenwho were born in the city and spent their pre-schoolyears there it is improbable that many were untraced.

(2) Birmingham contains no private institutionsfor the intellectually subnormal.

(3) Goodman and Tizard (1962), studying theprevalence of imbecility and idiocy in London andMiddlesex, found that few children attendingprivate institutions were unknown to the HealthDepartment. This finding was made in an area wherelocal authority ascertainment of subnormal children

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LOW INTELLIGENCE AND OBSTETRIC COMPLICATIONS

seems to present more difficulties than in Birming-ham, since 16 per cent. of mongols were not notifieduntil after the age of 10 years.

MEDICAL HISTORIESMedical histories of the subnormal children were

obtained from two sources: records made bymedical officers working for the Education andPublic Health Departments, and hospital records.

Since the children had lived in Birmingham fromthe time of birth until ascertainment, it seemedprobable that when they had visited hospitals,either as in-patients or as out-patients, they wouldusually have gone to hospitals within the city. Asearch was made for the name of each child in theindex register of every Birmingham hospital thatadmits or has clinics for children, and details of eachadmission or visit were inspected. 87 per cent. ofchildren who had been found unsuitable for edu-cation, and 52 per cent. of ESN children, had beenexamined by a paediatrician on one or moreoccasions. A further 6 and 19 per cent. respectivelyhad been seen by consultants in other specialties.The information obtained from these sources

enabled identification of 146 children who either hadconditions known to be associated with sub-normality, or had had diseases such as meningitis towhich subnormality can confidently be attributed.These 146 children (Table I) were removed from thesubnormal group whose records were analysed. The607 subnormal children who remained were regardedas having "non-specific" subnormality.

NORMAL SIBSNames, dates of birth, and school histories of all

sibs in the families of subnormal children wereobtained, but attention was restricted to sibs whobelong to the population being studied (i.e. childrenborn in Birmingham between 1950 and 1954(excluding multiple births) who remained in the cityuntil the age of 5 years). At the time of this inquiryall these children, excepting those born during thelast quarter of 1954, had become eligible to take the"11+" examination. The results of this examinationwere made available and the scores of sibs wereobtained.

Candidates have to take two verbal reasoning tests.These are a form of group intelligence test and theactual scores obtained are adjusted so that theaverage score is 100 and the standard deviation is 15.For the purposes of this study "normal intelligence"was defined as a mean score of 75 or more on the twotests. Such a score corresponds to one of about 80 ormore obtained on an individual intelligence test.

TABLE IPATHOLOGICAL CONDITIONS TO WHICH LOW

INTELLIGENCE IS AlTRIBUTED IN 146 OUT OF A GROUPOF 753 SUBNORMAL CHILDREN

Subnormal Children

Pathological Condition Unsuitable Edu-for cationaily Total

Education Subnormal

Mongolism .. .. .. 57 4 61Microcephaly . .20 4 24

r Tuberculous 1 3Meningococcal 1 4Influenzal . . 0 1

Meningitis Lymphocytic 0o Is 14Pyogenic, orgasmunidentified 1 0Unknown.. 2 0 J

Hydrocephalus .. 7 S 12Acute encephalopathies . . 7 4 IIDegenerative encephalopathies 1 0 1Cretinism 1 3 4Maternal rubella in first trimesterof pregnancy .. 3 0 3

Oxycephaly .. 1 2 3Encephalocele .. 2 0 2Head injury (followed by neuro-

logical signs of cerebraldamage) 1 2 3

Psychosis 2 0 2Laurence-Moon-Biedl-Bardetsyndrome .. 1 0 1

Turner's syndrome .. I 1 2Gargoylism .. I 0 1Phenylketonuria. . I 0 1Cerebral calcification ofunknown

cause .. 0 1 I

Total .il 35 146

* Microcephaly was defined as a head circumference of 3 or morestandard deviations below the average for the age and sex of the child.The figures of Westropp and Barber (1956) were used.

By this means 180 subnormal/normal sib pairswere identified for special study. Subnormal chil-dren who have normal sibs are not typical of sub-normal children as a whole (they differ for examplein parental fertility), and conclusions made fromcomparison of normal and subnormal sibs musttake account of this.

RESULTSThe 607 subnormal children have been divided

into three groups, according to their IQ: below 50;50 to 64; 65 to 74. A division has been made at 65because ascertainment of children above this level isknown to be incomplete. The division at 50 corre-sponds with the traditional demarcation betweenimbecility and feeblemindedness, and it has beenshown to separate, approximately, two groups ofsubnormal children who have important differences.The incidence of obstetric complications in the

three groups has been compared with that in thewhole population and in normal sibs.

ANTENATAL DISEASESTable II (overleaf) shows the incidence of toxae-

mia, non-toxic ante-partum haemorrhage (APH),

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TABLE IIINCIDENCE OF ANTENATAL DISEASE, BY IQ GROUP

Percentage withNo. with _

IQ Group No. of Details of Non-Children Pregnancy Tox- Toxic Anae- Pye-

Known aemia APH mia litis

Below SO 123 116 11*2 3 -4 4-3 1-7

50to64 198 186 8-1 1-6 7 0 2-2

65 to 74 286 272 6-6 1.5 6-2 1.1

WholePopulationof SingleBirths 73,687 68,846 90 19 4 8 1*7

anaemia, and pyelitis in pregnancies which precededthe births of the subnormal children; Table III showsthe incidence of the same diseases in pregnanciespreceding the births of the sib pairs (composed ofone normal and one subnormal child).

TABLE IIIINCIDENCE OF ANTENATAL DISEASES IN SIB PAIRS,

BY IQ GROUP

IQ of No. of No. withSub- Sib Sibs

normal Pairs Non-Sibs Tox- Toxic An- Pye-

aemia APH aemia litis

Below 50 32 Sub-normal 5 1 0 0Normal 5 1 1 0

50 to 64 54 Sub-normal 3 1 3 2Normal 5 0 2 0

65 to 74 94 Sub-normal 2 2 9 0Normal 4 6 5 3

In the compilation of the birth records, the coding"toxaemia" was applied to all cases of hypertensionor albuminuria during pregnancy. There is noapparent increase in the frequency of toxaemia inassociation with subnormality. But the incidence oftoxaemia in the population falls from 13-4 per cent.during first pregnancies to 7 2 per cent. duringsecond pregnancies, and the proportion of first-bornchildren in the subnormal group is smaller than inthe population. In Table IV the observed number ofpregnancies complicated by toxaemia and resultingin a subnormal child is compared with the numberwhich would be expected if the birth rank distri-bution of the subnormal children was the same asthat of the population. There is no evidence thattoxaenia and subnormality are associated.

Tables II and IHI show that there is no associationbetween non-toxic ante-partum haemorrhage and

TABLE IVOBSERVED INCIDENCE OF TOXAEMIA AND EXPECTEDINCIDENCE AFTER CORRECTION FOR BIRTH RANK,

BY IQ GROUP

No. with No. with ToxaemiaIQ Group Details of

Pregnancy Observed ExpectedKnown

Below 50 .. 116 13 11

50 to 64 .. 186 15 16

65 to 74 .. 272 18 23

subnormality. "Non-toxic antepartum haemor-rhage" is a description that was applied to ante-partum bleeding which resulted from many causesbut was not associated with toxaemia, and evensome cases of threatened abortion were classified inthis way. One can draw only the general conclusionthat disturbance of the placenta which results inbleeding during pregnancy, and which is not asso-ciated with toxaemia, does not lead to subnormalityin the foetus.

This conclusion can be made more specific in sofar as the inspection of delivery records enabled adistinction to be made between placenta praeviaand bleeding from other causes. Four pregnancieswhich resulted in subnormal children were compli-cated by placenta praevia (one child had an IQbelow 50, two had IQ's from 50 to 64, and one had anIQ between 65 and 74). This corresponds to anincidence of 6&6 per 1,000 children and may becompared with the incidence of 3*9 per 1,000confinements which Record (1956) estimated for thepopulation born in Birmingham between 1942 and1952. The excess of two subnormal children withplacenta praevia seems too small to justify a con-clusion that the conditions are associated.

All types of anaemia were grouped together as"anaemia" and measurements of the haemoglobinlevel and other blood indices were not recorded. Inthe IQ groups 50 to 64 and 65 to 74, there is a smallincrease in the number of children whose mothershad anaemia during pregnancy. In the population thefrequency of anaemia during pregnancy rises from3 8 per cent. in mothers of Social Classes I and H to6 0 per cent. in mothers of Social Classes IV and V.Allowing for the excess of the latter, the expectedincidence of anaemia in both subnormal groups is5-2 per cent., compared with the incidences of 7-0and 6 -2 per cent. that have been observed. There isalso a slight excess of subnormal sibs who resultedfrom pregnancies complicated by anaemia.

In Tables II and III there is no evidence of arelationship between "pyelitis" (a category that

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includes all non-tuberculous urinary tract infections)and intellectual subnormality.

PRESENTATION AT THE ONSET OF LABOURTable V shows the type of presentation at the

onset of labour. In each IQ group there is a smallexcess of breech presentations. This is partly a resultof the increased number of subnormal children whowere born before term, since in the population therewere 4 5 per cent. of breech presentations amongchildren who were born before the 38th week ofgestation and only 2 1 per cent. among those bornafter this time. But when an allowance has beenmade for the length of gestation, there remains anexcess of one breech presentation in each of the twolower IQ groups and an excess of four in the upperIQ group. The number of such presentations insubnormal sibs does not exceed that in normal ones(Table VI).

TABLE VTYPE OF PRESENTATION AT ONSET OF LABOUR, BY IQ

GROUPPercentage distribution

No. Type of Presentationwith

IQ TypeGroup of Pre- Occi- Caused

sent- Nor- pito- byation mal pos- Brow Face Breech Trans-Re- Vertex terior verse

corded Lie

Below 50 115 87-8 7-8 0.0 0.0 3 5 0 9

50 to 64 181 92-3 3-3 0 0 0-6 3-3 0-6

65 to 74 267 94-0 1-5 0-0 0-4 4.1 0.0

WholePopu-lationofSingleBirths 68,185 92-5 4-8 0-1 0-2 2-2 0-2

TABLE VIOCCIPITO-POSTERIOR AND BREECH PRESENTATIONS IN

SIB PAIRS, BY IQ GROUP

No. of PresentationsIQ Of No. of

Subnormal Sib Pairs Sibs Occipito- BreechSibs posterior

Below 50 32 Subnormal 1Normal 2

SO to 64 54 Subnormal 0Normal I 0

65 to 74 94 Subnormal 1 2Normal 3 4

Occipito-posterior presentation does not seem tobe associated with subnormality. Although there is asmall increase in the frequency of this presentation

in the lowest IQ group, the frequency in the othertwo groups is below that in the population. Amongsibs there are in every group fewer subnormal thannormal children who presented in this way (TableVI).

Neither face nor brow presentations, nor presen-tations caused by a transverse lie, are more frequentamong subnormal children.

TYPE OF LABOURThis was classified to show whether the onset was

spontaneous or induced, and whether delivery wasspontaneous, instrumental, or by Caesarean section.The results (Table VII) suggest that instrumental

delivery is not related to subnormality; but noallowance has been made for the association betweenthis method of delivery and primiparity. In thepopulation the percentage of instrumental deliveriesfalls from 8 * 8 in first births to 1 - 5 in second ones.After correction for the birth rank distribution ineach IQ group, there is no excess of these deliveriesamong subnormal children.

TABLE VIIMETHOD OF DELIVERY, BY IQ GROUP

Percentage distribution

No. with Method of DeliveryIQ Group Method of

Delivery Spon- Instru- Caesarean "Other"Recorded taneous mental Section

Below 50 117 92-3 4-3 2-6 0 9

50to64 189 93 1 2-1 3-2 1-6

65 to 74 277 96-0 111. 8 1I1

WholePopulationof SingleBirths 69,693 93 7 3*8 2-2 02

Similarly, although the results in Table VII suggestthat Caesarean section is not related to subnor-mality, a correction has to be made for the increase infrequency of Caesarean section from 1 * 3 per cent. inmothers under 20 to 6-1 per cent. in mothers over 40.After this correction there remains no evidence ofassociation between this method of delivery and sub-normality.

In the classification of type of labour a category"'other" denoted labours and deliveries which wereconsidered unusual. This category was not strictlydefined but its most frequent use was for labourswhich ended in breech extractions. Of the 163children in the population who were born after"other" types of labour seven are subnormal. Itseems unlikely that abnormal labour caused sub-normality in two of these seven children. One has five

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educationally subnormal sibs; the other has analatresia and was therefore damaged during earlyintra-uterine life. But none of the other five haseither a family history of subnormality or a con-genital defect, and it seems probable that theirlow intelligence is at least in part a consequence ofobstetric complications. Their birth histories aresummarized in Table VIII.

TABLE VIIICHILDREN DELIVERED BY "OTHER" METHODS

(TABLE VII, COL. 6), BY IQ GROUP

Birth Condition ofIQ Group Description of Antenatal Weight Child afterof Child History and Labour of Child Birth

(lb. oz.)

Below 50 Mother had rachitic flat pelvis. 2 12 RetrolentalThreatened abortion. Spon- fibroplasiataneous onset of labour at 29 Spastic diplegiaweeks. Cord prolapsed; inter-nal version and breech extrac-tion performed

50 to 64 Mother had flat pelvis and 3 1 Normalhistory of three previous mis-carriages and one stillbirth;labour precipitate at 38 weeks

65 to 74 Precipitate labour: child de- 8 0 Bruisedonheadlivered into a bucket Vomited blood

for 4 daysafter birth

Maternal and foetal distress 7 12 Described asduring second stage; breech showingextraction performed signs of

cerebralirritation

Toxaemia followed by eclamp- 6 1 Normaltic fit during second stage oflabour; breech extraction per-formed

ABSENCE OF A QUALIED BIRTH ATTENDANTThe observations on the type of attendant present

at the birth (for example hospital midwife or generalpractitioner) showed cases where birth had occurredbefore the arrival of a qualified attendant. Thishappened in 2-1 per cent. of births in the populationbut during the births of subnormal children it wasmore frequent (Table IX).

TABLE IXCHILDREN BORN IN THE ABSENCE OF A QUALIFIED

ATTENDANT, BY IQ GROUP

No. with Circum- Per cent. Born inIQ Group stances of Birth Absence of a

Recorded Qualified Attendant

Below 50 .. .. 122 2-5

50 to 64 .. .. 196 51

65 to 74 .. .. 285 6 7

Whole PopulationofSingle Births. . 73,062 2-1

Among the subnormal/normal sib pairs deliveryin the absence of a qualified attendant occurredmore often during the birth of the subnormal thanof the normal children (Table X).

TABLE XABSENCE OF QUALIFIED BIRTH ATTENDANT AND

CONDMON AFTER BIRTH IN SIB PAIRS, BY IQ GROUP

No. Born in No. withIQ of No. of Absence of Birth Injury

Subnormal Sib Pairs Sibs Qualified and/orSibs Birth Asphyxia

Attendant

Below 50 32 Subnormal 0 2Normal 1 0

50 to 64 54 Subnormal 5 3Normal 3 0

65 to 74 94 Subnormal 7 INormal 4

BIRTH INJURY AND ASPHYXIAA single coding was used to denote children who

showed signs of trauma or asphyxia at birth.Therefore children who for example had cephal-haematomata or were unusually cyanosed afterbirth were coded in the same way. It is possible tomake only general conclusions from such data.Nevertheless the excess of subnormal children with"birth injury and/or asphyxia" is striking. It ispresent in all IQ groups (Table XI), and it also showsin the comparison between normal and subnormalsibs (Table X). Table XII gives details of the con-dition at birth of subnormal children with birthinjury and/or asphyxia.

TABLE XIINCIDENCE OF "BIRTH INJURY AND/OR ASPHYXIA",

BY IQ GROUP

No. whose Condition Per cent. with BirthIQ Group at Birth was Recorded Injury and/or

Asphyxia

Below 50 .. .. 117 6-8

50to64 .. .. 191 5-2

65 to 74 .. .. 282 3-5

Whole Populationof Single Births 69,841 2-2

TABLE XIIANALYSIS OF SUBNORMAL CHILDREN WITH "BIRTH

INJURY AND/OR ASPHYXIA", BY IQ GROUP

Description of IQ GroupChild's Condition

Below 50 50 to 64 65 to 74 Total

Cephalhaematoma .. 1 2 1 4White asphyxia .. 0 1 1 2Cerebral irritation .. 0 1 2 3Cyanosis (with or with-

out convulsions) .. 6 3 4 13Unspecified .. .. 1 3 2 6

Total .. .. 8 10 10 28

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DIscussIoNThese results suggest that recognized compli-

cations of pregnancy and labour play little part in theaetiology of low intelligence. They confirm thefindings of Fairweather and Mllsley (1960), but theydo not support the conclusion of Pasamanick andLiienfeld (1955) that toxaemia and bleeding duringpregnancy cause low intelligence.

There was a small increase in the incidence ofanaemia during pregnancies which preceded thebirths of children with IQ's above 50. This increasepersisted after adjustment to allow for the asso-ciation of anaemia with Social Class. But correctionfor Social Class probably does not make adequateallowance for the unusual social circumstances ofmany of the families of mildly subnormal children;and the data do not justify conclusions about theassociation between anaemia and subnormality.A small excess of breech presentations was found

in each IQ group; but among sibs breech presen-tations were not more frequent for subnormal thanfor normal children. Breech delivery may be a rarecause of subnormality. Among subnormal childrenwith IQs above 50, the excess of unsupervised birthswas quite marked, and subnormal sibs were moreoften affected than normal ones. However, many ofthe parents of these children are themselves of lowintelligence, and they may delay before they call amidwife. Therefore, while an unsupervised deliverycould lead to cerebral damage and consequent sub-normality, it may be that the absence of a qualifiedassistant at the birth of a subnormal child onlyreflects the low intelligence of the family Into whichthe child is born.There is evidence that recognized obstetric

complications have contributed to the low intelli-gence of the five children described in Table VIIIand perhaps of a small number of children who weredelivered as breeches or in the absence of a qualifiedattendant. These do not account for the excess ofsubnormal children recorded as showing signs ofbirth injury or asphyxia: there remains a small groupwhose birth was uncomplicated, who did not showfrank signs of trauma such as cephalhaematomata,but who showed signs which might have reflectedeither the effects of asphyxia during birth or theconsequences of damage to the brain sustained atsome stage before the onset of labour.

SUMMARY607 children with subnormal intelligence of

unknown cause were identified in a population of73,687 single births for whom obstetric data hadbeen recorded.

Recognized abnormalities of pregnancy anddelivery seemed to play little part in determiningsubnormality. The births of five children wereassociated with unusual obstetric complications andthree other children had cephalhaematomata-direct evidence of birth injury.There was a small excess of breech presentations

among subnormal children, and subnormality abovean IQ of 50 was associated with a slightly increasedincidence of anaemia of pregnancy and delivery inthe absence of a qualified attendant. The aetiologicalsignificance of these factors was not established.

Contrary to findings in other enquiries there wasno evidence that toxaemia or ante-partum haemor-rhage caused subnormality.

It is a pleasure to thank those who have helped in thisstudy. Dr E. L. M. Millar, Medical Officer of Health forBirmingham, and Sir Lionel Russell, Chief EducationOfficer for Birmingham, permitted the use of records intheir departments. Dr P. R. Kemp, Assistant SeniorSchool Medical Officer, Mr W. J. Bannon, SeniorEducational Psychologist, Dr J. E. Reiner, EducationalPsychologist, and Mr A. Marrington, Chief MentalWelfare Officer, gave advice and assistance. Mr L.Rankin, Superintendent of Education and AttendanceOfficers, provided information about the sibs of the sub-normal children.

I am especially grateful to Miss Gillian Davis who wasresponsible for much of the work involved in the col-lection and analysis of the data.

REFERENCESCharles, E. (1951). Brit. J. soc. Med., 5, 41.Dayton, N. A. (1930). New Engl. med. J., 203, 398.Fairweather, D. V. I., and llsley, R. (1960). Brit. J. prev.

soc. Med., 14,149.Goodman, N., and Tizard, J. (1962). Brit. med. J., 1, 216.Pasamanick, B., and Lilienfeld, A. M. (1955). J. Amer.

med. Ass., 159, 155.Penrose, L. S. (1963). "The Biology of Mental Defect",

3rd ed. Sidgwick and Jackson. London.Rauramo, L., Gronroos, M., and Kivikoski, A. (1961).Acta obstet. gynaec. scand., 40, 321.

Record, R. G. (1956). Brit. J. prev. soc. Med., 10, 19.Stott, D. H. (1957). Lancet, 1, 1006.Westropp, C. K., and Barber, C. R. (1956). J. Neurol.

Neurosurg. Psychiat., 19, 52.

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