Maternal smoking during pregnancy and intellectual performance in young adult Swedish male offspring
Smoking during pregnancy has been linked to an increased risk of several adverse birth outcomes. Associations with deficits in cognitive development have also been suggested. It is unclear whether these associations are due to genetic and/or environmental confounding. In a population-based Swedish cohort study on 205,777 singleton males born to Nordic mothers between 1983 and 1988, we examined the association between maternal smoking during pregnancy and the risk of poor intellectual performance in young adult male offspring. In the cohort analyses, the risk of poor intellectual performance was increased in sons of smoking mothers compared with sons of non-smokers. Stratifying for maternal smoking habits across two pregnancies, there was an increased risk of poor intellectual performance for both sons if the mother was only smoking in the first pregnancy, but in neither son if the mother was only smoking in the second pregnancy. The effect of smoking during pregnancy on intellectual performance was not present when the association was evaluated within sibling pairs. Thus, the association between prenatal smoking exposure and offspring risk of low intellectual performance appears to be completely confounded by familial (genetic and early environmental) factors.
[Show abstract] [Hide abstract] ABSTRACT: Prenatal exposure to substances of abuse is associated with numerous psychological problems in offspring, but quasi-experimental studies controlling for co-occurring risk factors suggest that familial factors (e.g., genetic and environmental effects shared among siblings) confound many associations with maternal smoking during pregnancy (SDP). Few of the quasi-experimental studies in this area have explored normative psychological traits in early childhood or developmental changes across the lifespan, however. The current study used multilevel growth curve models with a large, nationally-representative sample in the United States to investigate for potential effects of SDP on the developmental trajectories of cognitive functioning, temperament/personality, and disruptive behavior across childhood, while accounting for shared familial confounds by comparing differentially exposed siblings and statistically controlling for offspring-specific covariates. Maternal SDP predicted the intercept (but not change over time) for all cognitive and externalizing outcomes. Accounting for familial confounds, however, attenuated the association between SDP exposure and all outcomes, except the intercept (age 5) for reading recognition. These findings, which are commensurate with previous quasi-experimental research on more severe indices of adolescent and adult problems, suggest that the associations between SDP and developmental traits in childhood are due primarily to confounding factors and not a causal association.
- "In contrast, quasi-experimental studies, which use design features to rule out confounding factors rather than statistical controls, suggest unmeasured confounds better explain the statistical associations between maternal substance use during pregnancy and offspring psychosocial problems (Knopik 2009; D'Onofrio et al. 2013 ). For example, siblingcomparison studies, which compare siblings differentially exposed to maternal substance use during pregnancy (for a review of the sibling-comaprison approach, see Lahey and D'Onofrio 2010) suggest that the statistical association between maternal SDP and cognitive functioning (Gilman et al. 2008a, b; Lundberg et al. 2010; D'Onofrio et al. 2010a, b), externalizing outcomes (Lindblad and Hjern 2010), delinquency (D'Onofrio et al. 2010a, b; D'Onofrio et al. 2012), stress-coping (Kuja-Halkola et al. 2010), and other indices of adjustment are due to confounding factors, not the specific influences of SDP. Further, in vitro fertilization studies, in which mothers are not genetically related to the offspring but provide the prenatal and postnatal environments , also suggest that the association between maternal SDP and offspring conduct problems (Rice et al. 2009) and ADHD (Thapar et al. 2009) are due to confounding factors, notably genetic factors passed down from mothers to their offspring. "
[Show abstract] [Hide abstract] ABSTRACT: Studies on adverse childhood health and development outcomes associated with parental smoking have shown inconsistent results. Using a cohort of Belarusian children, we examined differences in cognition, behaviors, growth, adiposity, and blood pressure at 6.5 years according to prenatal and postnatal exposure to parental smoking. Using cluster-adjusted multivariable regression, effects of exposure to prenatal smoking were examined by comparing (1) children whose mothers smoked during pregnancy with those of mothers who smoked neither during nor after pregnancy and (2) children whose mothers smoked during and after pregnancy with those whose mothers smoked after pregnancy only; effects of postnatal smoking were examined by comparing (1) children whose mothers smoked after pregnancy only with those of mothers who smoked neither during nor after pregnancy and (2) children whose fathers smoked with those whose fathers did not smoke among children of non-smoking mothers after adjusting for a wide range of socioeconomic and family characteristics. After adjusting for confounders, children exposed vs unexposed to prenatal maternal smoking had no differences in mean IQ, teacher-rated behavioral problems, adiposity, or blood pressure. Children exposed to maternal postnatal smoking had slightly increased behavioral problems [0.9, 95% CI: 0.6, 1.2 for total difficulties], higher body mass index [0.2, 95% CI: 0.1, 0.3], greater total skinfold thickness [0.4, 95% CI: 0.04, 0.71], and higher odds of overweight or obesity [1.4, 95 % CI; 1.1, 1.7]. Similar magnitudes of association were observed with postnatal paternal smoking. No adverse cognitive, behavioral and developmental outcomes were associated with exposure to maternal prenatal smoking. Observed associations with postnatal smoking of both parents may reflect residual confounding by genetic and family environmental factors.
- "Although results from previous studies are inconsistent, our results confirm those of studies that rigorously controlled for confounding factors [16,3839404142. In particular, family-based studies that compared siblings born to the same mothers with discrepant smoking status across pregnancies (to minimize residual confounding by unmeasured family factors) have reported no differences in cognitive ability, externalizing behaviors, or overweight/obesity within siblings383940 . Other studies based on large cohorts of children have reported that maternal and paternal smoking during pregnancy are associated to a similar degree with offspring cognitive outcomes  and blood pressure . "
[Show abstract] [Hide abstract] ABSTRACT: The aim of the study was to examine the effects of tobacco smoking in pregnancy on children's IQ at the age of 5. A prospective follow-up study was conducted on 1,782 women, and their offspring were sampled from the Danish National Birth Cohort. At 5 years of age, the children were tested with the Wechsler Preschool and Primary Scale of Intelligence-Revised. Parental education, maternal IQ, maternal alcohol consumption in pregnancy, the sex and age of the child, and tester were considered core confounders, but the full model also controlled for prenatal paternal smoking, maternal age and Bodymass Mass Index, parity, family/home environment, postnatal parental smoking, breast feeding, the child's health status, and indicators for hearing and vision impairments. Unadjusted analyses showed a statistically significant decrement of 4 points on full-scale IQ (FSIQ) associated with smoking 10+ cigarettes per day compared to nonsmoking. After adjustment for potential confounders, no significant effects of prenatal exposure to tobacco smoking were found. Considering the indisputable teratogenic effects of tobacco smoking, these findings should be interpreted with caution. Still, the results may indicate that previous studies that failed to control for important confounders, particularly maternal intelligence, may be subject to substantial residual confounding.
- "The overall results of the present study are thus in line with previous studies in which statistical adjustment of potentially confounding factors eliminated an apparent effect of smoking exposure on IQ [21–24, 26, 40–43]. Lundberg et al.  addressed the causal effect of prenatal smoking exposure by comparing the intellectual performance (as measured by a military draft board test) of 14,722 pairs of full siblings, only one of which had been exposed to smoking in utero. There were no differences between exposed and unexposed siblings but an increased risk of low test performance for both if the mother had smoked only during her first pregnancy and no difference compared to nonexposed controls for either sibling if she had smoked only during her second. "
Discover cutting-edge research
ResearchGate is where you can find and access the latest publications from your field of research.Discover more