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SUMMARYMean V.R. (verbal reasoning) scores recorded in the eleven‐plus examination for Birmingham multiple births in the years 1950‐57 were 95‐7 for 2164 twins and 91‐6 for 33 triplets. The mean for 48,913 single children born in the years 1950‐54 was 100‐1.The low scores of twins are not explained by differences from single births in their distributions by maternal age and birth order or by birth weight and duration of gestation. They are also not accounted for by the increased risks associated with monozygosity (assessed by comparison of like‐ and unlike‐sex twins) or with delivery of the second twin. Taken together these observations, like the previous ones on single births, suggest that variation in experience before and during birth has little influence on measured intelligence and that the explanation of the large difference between twins and single children must be sought in the postnatal environment.There were 148 twins whose co‐twins were stillborn or died within 4 weeks after birth; their mean score was 98‐8, only a little lower than that of single births (99‐5) standardized to the maternal age and birth rank distribution of twins. From this evidence it is concluded that the handicapping of twins, reflected in their low verbal reasoning scores, is due to postnatal rather than prenatal influences.These conclusions are of course based on children who took the eleven‐plus examination and cannot be accepted without reservations for those who did not.

1. Observations on foetal growth in human pregnancy are recorded on 22,454 single, 325 twin, 249 triplet and 27 quadruplet maternities. 2. Mean birth weights of singletons, twins, triplets and quadruplets are respectively 7\m=.\43, 5\m=.\27,4\m=.\00and 3\m=.\07lb. 3. For single, twin, triplet and quadruplet pregnancies, mean durations of gestation (in days) are 280\m=.\5,261\m=.\6,246\m=.\8 and 236\m=.\8.4. Mean birth weight is greater for small than for large litters even when comparison is restricted to births delivered after the same period of gestation (see Table 4).5. It is suggested that these observations, which are in accord with reports on experimental animals, raise two questions: (a) why is foetal growth retarded in multiple pregnancy during the last weeks of gestation? and (b) why is onset of labour earlier in multiple than in single pregnancy ?6. In consideration of 5 (a) it is shown that:(i) Mean foetal weight appears to be independent of litter size until about the 27th week of gestation.(ii) The rate of growth of multiple foetuses is slower than that of single foetuses from a stage of gestation which varies with size of litter as follows: quadruplets from about 26 weeks ; triplets from 27 weeks; and twins from 30 weeks. In the case of singletons, foetal growth is linear between 30 and 36 weeks; after 36 weeks the rate of growth is reduced.(iii) At the times from which the respective rates of foetal growth are retarded, mean litter weights of twins, triplets and quadruplets are approximately the same. These mean litter weights (in lb.) are: quadruplets at 26 weeks, 7\m=.\6;triplets at 27 weeks, 6\m=.\9;twins at 30 weeks, 6\m=.\9.The mean weight of single births at 36 weeks is 6\m=.\5lb.(iv) From the time that foetal growth is retarded, litter weight increment is approximately the same for every size of litter. Support is provided for the view that (a) retardation of foetal growth in large litters is attributable, at least in part, to crowding in the uterus (see Table 6); and (b) the restriction on foetal growth in the crowded uterus may be imposed by the placenta (see Table 7). 7. In consideration of 5 (b) it is shown that mean litter weights of singletons, twins, triplets and quadruplets at birth are respectively 7\m=.\43,10\m=.\53,12\m=.\00 and 12\m=.\28lb. It is suggested that these observations are not inconsistent with the view that the early onset of labour in multiple pregnancy is due to distension of the uterus, if we suppose that the amount of distension which the uterus will tolerate during the last weeks of gestation decreases as pregnancy advances.8. Mean litter weights of multiple births increase with birth order.Variation in mean birth weight in association with litter size has been recorded for many species ; it is due to differences between small and large litters (a) in the length of gestation, and (6) in the rate of foetal growth in late pregnancy. Observations on man have hitherto been restricted to comparison of twins and single births. Our objects in this communication are to p...

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There have been two main approaches to investigation of the relation of birth weight to intelligence. In one, birth weights of children of low intelligence are compared with those of children of average or high intelligence. Where the comparison has been between children in ordinary schools, as in Ascher & Roberts's study (1949) in primary, grammar and secondary schools, birth weight differences have usually been unimpressive or absent ; but among the subnormal, mean birth weight appears to be reduced and the reduction is present even after exclusion of those whose low intelligence is associated with physical abnormalities (Barker, 1966).