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

Abstract

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.

Keywords:

• maternal smoking
• tobacco exposure
• child growth
• head circumference
• weight
• height

Acknowledgments

We thank statisticians Marja-Leena Lamidi M.Sc. and Tuomas Selander M.Sc. for their valuable advice on statistical analyses.

Abbreviations

BMI, body-mass index; HC, head circumference; ICD-10, International Classification of Diseases, 10th version; SES, socioeconomic status; SDS, standard deviation score.

Statement on Ethics

This register-based study has been approved by the ethics committee of the Northern Savo Hospital District (DNr 64/2010) and permissions have been obtained from the register holders, the National Institute for Health and Welfare (THL/582/5.05.00/2009;

THL/504/5.05.00/2010;THL/1010/5.05.00/2018), Statistics Finland (TK-53-839-18/u1183_a) and Espoo Municipality Institutional Review Board (4.9.2008/DNo 1224).

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This work was supported by Arvo and Lea Ylppö Foundation, Päivikki and Sakari Sohlberg Foundation, Finnish Medical Foundation, Kuopio University Hospital, State Research Funding and National Graduate School of Clinical Research.