Impact of maternal smoking on birth size: effect of parity and sex dimorphism.

BACKGROUND

Maternal smoking during pregnancy causes a delay of intrauterine growth.

OBJECTIVE

To examine the effect of maternal smoking during pregnancy on fetal growth in relationship to maternal parity, age and number of cigarettes smoked/day, and offspring's gender.

SUBJECTS

We studied 2,108 term newborns (1,102 male, 1,006 female) delivered at the General University Hospital of Patras from 1994 to 2004. The 1,443 were born to mothers who did not smoke and 665 to mothers who smoked during pregnancy.

METHODS

Birth weight, length and head circumference were measured prospectively in all newborns. Also, maternal smoking status and number of cigarettes smoked per day, age, and parity were recorded. For the analysis, t test, one-way ANOVA, Mann-Whitney U test, Spearman rank correlation, and factorial MANOVA with covariates were used.

RESULTS

With increasing parity, in the neonates of nonsmoking mothers there was a gradual increase of growth, whereas in neonates of smoking mothers there was a gradual decrease of growth. This effect was more pronounced in males. A significant negative main effect on growth resulted from the interaction of smoking with parity (p = 0.013), and with gender and parity (p = 0.001). There was a significant negative correlation between number of cigarettes smoked per day and growth, the strength of which increased with parity, mainly in males.

CONCLUSION

Maternal smoking during pregnancy causes a delay in fetal growth, which is greater in male offspring, an effect that is enhanced with parity but is independent of maternal age.