Correlations of birth weight and gestational age across generations.

Maternal birth weight is known to be a predictor of offspring birth weight. Less is known about the recurrence of gestational age. In order to estimate the recurrence risk of low birth weight and preterm birth across generations in a population-based sample, 11,092 pairs of mother-firstborn offspring were obtained through an internal linkage in the Norwegian Birth Registry based on the years 1967-1969 (mothers) and 1986-1989 (offspring). A low correlation coefficient of 0.086 was found for gestational age across generations, whereas the correlation between maternal and offspring birth weight was 0.242. Mothers with birth weight below 2500 g had a significantly increased risk (odds ratio = 3.03, 95% conf. interval 1.79-5.11) of having a low birth weight child compared with mothers with birth weight above 4 kg. On the other hand, if the mother was born before the 37th completed week of gestation, the risk of having a preterm child was not significantly increased (odds ratio = 1.46, conf. interval 0.96-2.21) compared with mothers who were born at term. Thus, in contrast to birth weight, human variation in gestational age does not appear to be influenced by genetic factors to any large degree.