Maternal Smoking During Pregnancy and Offspring Head Growth in Comparison to Height and Weight Growth Up to 6 Years of Age: A Longitudinal Study.

Background: Maternal smoking during pregnancy causes fetal growth retardation. Thereafter, it has been associated with excessive childhood weight gain and decreased linear growth in the offspring. However, it is not known whether head circumference (HC), the surrogate of brain size in childhood, is altered after intrauterine tobacco exposure. We assessed the association of maternal smoking during pregnancy with offspring HC growth up to age 6 years in comparison with length/height growth and weight gain.

Methods: We combined data from Medical Birth Register and longitudinal growth data from primary care of 43,632 children (born 2004-2017). Linear mixed effects models were used for modeling, adjusting for potential perinatal and socioeconomic confounders.

Results: At birth, maternal smoking during pregnancy was associated with a mean deficit of 0.19 standard deviation score (SDS) (95% CI: -0.25, -0.12) in HC, -0.38 SDS (95% CI: -0.43, -0.32) in length, and -0.08 SDS (95% CI:-0.14, -0.02) in weight-for-length. HC in smokers' children failed to catch up to that of non-smokers' children. Height of smokers' infants reached that of non-smokers' infants by 12 months but declined thereafter. Weight-for-height of smokers' infants exceeded the level of non-smokers' infants at 3 months and remained significantly elevated thereafter. HC in the offspring of mothers who quit smoking in the first trimester was not deficient, but their weight-for-height was elevated.

Conclusion: HC of smokers' children is still deficient at age 6 years. Since most of the head growth occurs during the first 2 years of life, the defect may be permanent. In smokers' children, weight gain was excessive up to 6 years and height was deficient at 6 years consistent with previous literature. Efforts should be made to encourage pregnant women to quit smoking in the beginning of the pregnancy.