Smoking in pregnancy and development into early adulthood.

Follow up analyses of data on the 1958 cohort from the national child development study have shown that the association of smoking in pregnancy with physical and intellectual development diverges between the sexes at age 16, no longer being significantly associated with height in girls. These studies, however, have emphasised that the differences in outcome are small and may be explained by other factors. The analyses have taken account of birth weight and have therefore examined the effects of smoking on subsequent development in addition to this variable. To assess the importance of smoking on development in early adult life and whether the effect is independent of birth weight data from the 1958 cohort at age 23 were analysed. Only weak evidence for a relation between smoking in pregnancy and self reported height of the offspring was apparent once social class, size of family, mothers' height, and birth weight for gestational age were taken into account. After omission of birth weight from the analyses, however, the average difference in height between subjects whose mothers smoked 20 cigarettes a day or more during the second half of pregnancy and those whose mothers did not was 0.93 cm in men and 1.83 cm in women. A strong association was also evident with the highest qualification achieved by subjects at this age, suggesting a long term relation between smoking in pregnancy and the intellectual development of the offspring.