Maternal smoking during pregnancy and intellectual performance in young adult Swedish male offspring

Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Paediatric and Perinatal Epidemiology (Impact Factor: 3.13). 01/2010; 24(1):79-87. DOI: 10.1111/j.1365-3016.2009.01073.x
Source: PubMed


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.

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    • "Although results from previous studies are inconsistent, our results confirm those of studies that rigorously controlled for confounding factors [16,38-42]. 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 siblings [38-40]. 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 [41] and blood pressure [42]. "
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    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.
    Full-text · Article · Jul 2013 · BMC Pediatrics
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    • "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. [44] 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. "
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    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.
    Full-text · Article · Dec 2012 · Journal of pregnancy
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    • "On the other hand, examination of siblings pairs where the mother smoked during one pregnancy but not the other also identified an elevation in school problems for both children which indicated that nonsmoking factors were responsible (Lambe et al., 2006). The same general pattern indicative of unmeasured genetic or environmental variables underlying intellectual performance deficits was subsequently replicated in an older all-male sample (Lundberg et al., 2010), indicating that the relationship between in utero nicotine exposure and school performance may be dependent on the sample characteristics. "
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    ABSTRACT: Smoking tobacco during pregnancy results in exposure to the fetal neuroteratogen nicotine. The current study evaluated if the offspring of smokers show abnormalities in maternal ratings of executive function, prevalence of Attention Deficit Hyperactivity Disorder (ADHD), and academic performance. A secondary objective was to determine the utility of online data collection. Mothers (N = 357) completed the parent form of the Behavioral Rating Inventory of Executive Function (BRIEF) and provided information about smoking during pregnancy. The internal consistency of the BRIEF when administered electronically was quite satisfactory (Cronbach's α = .98). As anticipated, ADHD was more frequently diagnosed in the offspring of women that smoked at least 10 cigarettes/day (odds ratio [OR] = 2.64, 95% CI = 1.22-5.71). Higher (i.e., more problematic) ratings relative to unexposed children (p < .01) were only identified on the total BRIEF score, the Metacognition Index, and on the Initiate, Plan/Organize, and Monitor scales among children exposed to ≥10 cigarettes/day. Nicotine-exposed children were also more likely to perform less well than their classmates in math (OR = 2.78, 95% CI = 1.59-4.87) and reading (OR = 2.00, 95% CI = 1.10-3.63), and these academic effects were independent of maternal education levels. This report provides preliminary evidence that the BRIEF has adequate psychometric properties when administered electronically and that mothers who smoke have offspring with lower executive function proficiency. These findings contribute to a larger literature that indicates that smoking during pregnancy results in adverse reproductive outcomes and, possibly, subtle but enduring deficits in prefrontal function.
    Preview · Article · Feb 2012 · Nicotine & Tobacco Research
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