Birthweights in consecutive pregnancies.

Abstract

Summary An analysis was made of birthweights in consecutive pregnancies among 6702 married women who were mostly followed up for ten years or more after the first viable birth. To facilitate comparisons between pregnancies, birthweights were standardized for sex and to 40 weeks gestation. The second baby was heavier than the first in 60 per cent of women; in third or later pregnancies, the chances of a baby being heavier or lighter than its predecessor were about equal. When the reproductive history began with one or more spontaneous abortions, birthweights in subsequent pregnancies appeared to be unaffected: but when the first pregnancy ended in stillbirth, birthweights in subsequent pregnancies tended to be considerably reduced. Individual women had a low but highly significant tendency to have pregnancies of similar gestational length, and the full-sib coefficient of correlation between adjusted birthweights was 0.53. The similarity of birthweights within sibships could not be explained on grounds of maternal size. Birthweights in consecutive pregnancies tended to rise with increase of maternal weight between pregnancies and with greater gains of weight during pregnancy.