Intergenerational studies of human birthweight from the 1958 birth cohort. II. Do parents who were twins have babies as heavy as those born to singletons?
OBJECTIVE
To ascertain whether maternal twinning influences the previously described association between the birthweight of singleton mothers and their infants.


METHODS
The association between the birthweight of singleton parents and their offspring and that between twin parents and their offspring was compared using data from the 23-year-old sample of the 1958 British national birth cohort. The numbers available for full comparison were 1027 female and 611 male singleton cohort members, and 26 female and 17 male twin cohort members and their first singleton livebirths.


RESULTS
Of the mothers who had been twins, half had been of low birthweight, and overall their mean weight was 700 g less than that of their singleton counterparts. Nevertheless, the mean birthweight of babies of twin mothers was 133 g, and of twin fathers 94 g, greater than of babies of corresponding singletons. For female, but not male, parents this difference persisted after adjustment for confounding variables.


CONCLUSIONS
We suggest two possible reasons for the difference between the weight of babies of twin and singleton mothers. Firstly, the growth of twins becomes retarded late in pregnancy, possibly after a period critical in determining long-term reproductive effects. Secondly, the twin survivors were of higher birthweight than the original twin cohort, whilst the singleton survivors were more representative of all singleton births, thus introducing a possible bias.
Emanuel
I
I
Department of Epidemiology, University of Washington.
Filakti
H
H
Alberman
E
E
Evans
S J
SJ
D001724:Birth Weight; D015331:Cohort Studies; D005192:Family Health; D005220:Fathers; D005260:Female; D005500:Follow-Up Studies; D005865:Gestational Age; D006801:Humans; D008297:Male; D009035:Mothers; D014427:Twins; D006113:United Kingdom