A quasi-experimental study of maternal smoking during pregnancy and offspring academic achievement.

Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN 47405, USA.
Child Development (Impact Factor: 4.92). 01/2010; 81(1):80-100. DOI: 10.1111/j.1467-8624.2009.01382.x
Source: PubMed

ABSTRACT The current study, based on all births in Sweden from 1983 to 1991 (N = 654,707), explored the processes underlying the association between smoking during pregnancy (SDP) and offspring school grades and mathematic proficiency at age 15. The analyses compared relatives who varied in their exposure to SDP and who varied in their genetic relatedness. Although SDP was statistically associated with academic achievement (AA) when comparing unrelated individuals, the results suggest that SDP does not cause poorer academic performance, as full siblings differentially exposed to SDP did not differ in their academic scores. The pattern of results suggests that genetic factors shared by parents and their offspring help explain why offspring exposed to SDP have lower levels of AA.

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    ABSTRACT: Maternal smoking during pregnancy (SDP) has been associated with several psychiatric outcomes in the offspring; studies have questioned whether the associations are causal, however. We analyzed all children born in Sweden between 1983 and 2009 to investigate the effect of SDP on multiple indicators of adverse outcomes in three areas: pregnancy outcomes (birth weight, preterm birth and being born small for gestational age), long-term cognitive abilities (low academic achievement and general cognitive ability) and externalizing behaviors (criminal conviction, violent criminal conviction and drug misuse). SDP was associated with all outcomes. Within-family analyses of the pregnancy outcomes were consistent with a causal interpretation as the associations persisted when siblings discordant for SDP were compared. For the cognitive and externalizing outcomes, the results were not consistent with causal effects; when comparing differentially exposed siblings none of the associations remained significant. In quantitative genetic models genetic factors explained the majority of the associations between SDP and cognitive and externalizing outcomes. The results suggest that the associations between SDP in mothers and cognition and externalizing behaviors in their offspring is primarily due to genetic effects that influence the behaviors in both generations.
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    ABSTRACT: Background Maternal Smoking During Pregnancy (SDP) has consistently been associated with increased risk of attention-deficit/hyperactivity disorder (ADHD) in offspring, but recent studies indicate that this association might be due to unmeasured familial confounding. MethodsA total of 813,030 individuals born in Sweden between 1992 and 2000 were included in this nationwide population-based cohort study. Data on maternal SDP and ADHD diagnosis were obtained from national registers and patients were followed up from the age of 3 to the end of 2009. Hazard Ratios (HRs) were estimated using stratified Cox regression models. Cousin and sibling data were used to control for unmeasured familial confounding. ResultsAt the population level maternal SDP predicted ADHD in offspring (HRModerateSDP=1.89; HRHighSDP=2.50). This estimate gradually attenuated toward the null when adjusting for measured confounders (HRModerateSDP=1.62; HRHighSDP=2.04), unmeasured confounders shared within the extended family (i.e., cousin comparison) (HRModerateSDP=1.45; HRHighSDP=1.69), and unmeasured confounders within the nuclear family (i.e., sibling comparison) (HRModerateSDP=0.88; HRHighSDP=0.84). Conclusions Our results suggest that the association between maternal SDP and offspring ADHD are due to unmeasured familial confounding.
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May 22, 2014