Smoking in pregnancy and development into early adulthood.
Authors: K. R. Fogelman, O. Manor
Journal: BMJ (1988)

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.Data from the UK National Child Development Study have indicated an association between smoking during pregnancy and subsequent physical and intellectual child development. To determine whether these effects persist into early adulthood, the 1958 birth cohort was studied when members were 23 years of age. Of the 8200 young adults included, 32% had mothers who had smoked during their gestation. The unadjusted difference in the average height of men whose mothers had not smoked and those whose mothers had smoked 20 cigarettes/day or more was 1.42 cm. Adjustment for independent variables (social class, father's occupation, birth weight, maternal height, family size) reduced this difference to 0.5 cm, which is not significant. When birthweight was omitted from the analysis, the adjusted difference was 0.93, which is of marginal statistical significance. In women, the respective differences in height were larger--2.53 cm, 1.57 cm, and 1.83 cm. Thus, these analyses provide little support for an association of physical growth and maternal smoking during pregnancy when social class, family size, birth weight for gestational age, and maternal height are taken into account. This finding is in contrast with analyses conducted on this birth cohort at ages 7 and 11 years, when smoking was significantly relative to the children's height and their achievements in reading and mathematics. It is hypothesized that smoking in pregnancy either affects the rate of growth but not total growth (achieved around years of age) or it affects growth until puberty, when the greater changes occurring at this stage because the effect of maternal smoking.