The Effect of Smoking during Pregnancy on Severity and Directionality of Externalizing and Internalizing Symptoms: A Genetically Informed Approach.

Mikael O Ekblad,Rohan H C Palmer,Emily Rolan,Alexandre Todorov,Valerie S Knopik,Kristine Marceau,Andrew C Heath

doi:10.3390/ijerph17217921

Abstract

The objective was to examine the association between maternal smoking during pregnancy (SDP) and (I) severity and (II) directionality of externalizing and internalizing symptoms in a sample of sibling pairs while rigorously controlling for familial confounds. The Missouri Mothers and Their Children Study is a family study (N = 173 families) with sibling pairs (aged 7 to 16 years) who are discordant for exposure to SDP. This sibling comparison study is designed to disentangle the effects of SDP from familial confounds. An SDP severity score was created for each child using a combination of SDP indicators (timing, duration, and amount). Principal component analysis of externalizing and internalizing behavior, assessed with the Child Behavior Checklist and Teacher Report Form, was used to create symptom severity and directionality scores. The variance in severity and directionality scores was primarily a function of differences between siblings (71% and 85%, respectively) rather than differences across families (29% and 15%, respectively). The severity score that combines externalizing and internalizing symptom severity was not associated with SDP. However, a significant within-family effect of SDP on symptom directionality (b = 0.07, p = 0.04) was observed in the sibling comparison model. The positive directionality score indicates that SDP is associated with differentiation of symptoms towards externalizing rather than internalizing symptoms after controlling for familial confounds with a sibling comparison model. This supports a potentially causal relationship between SDP and externalizing behavior.

Highlights

Maternal smoking during pregnancy (SDP) remains one of the most common environmental exposures compromising fetal health
There was no effect of SDP on the severity score, meaning that SDP did not associate with combined symptom severity of externalizing and internalizing behavior
That SDP predicted differentiation towards externalizing symptoms is consistent with the generalist gene and specialist environments hypothesis, which suggests that genetic influences should be more predictive of severity of problems and comorbidity, whereas environmental influences should explain their divergence [28,46,47]

Summary

Introduction

Maternal smoking during pregnancy (SDP) remains one of the most common environmental exposures compromising fetal health. Despite a decreasing trend of SDP in most developed countries, research suggests that young and low-educated women continue to be at a higher risk for SDP and over 50% of women who smoke during early pregnancy continue to smoke throughout pregnancy [1]. SDP is associated with multiple adverse pregnancy complications [2] as well as prenatal and. Res. Public Health 2020, 17, 7921; doi:10.3390/ijerph17217921 www.mdpi.com/journal/ijerph

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