Familial confounding of the association between maternal smoking in pregnancy and autism spectrum disorder in offspring.
Amy E Kalkbrenner, Sandra M Meier, Paul Madley-Dowd and 4 others
PMID 31464107WHAT IT FOUND
Maternal smoking in pregnancy is not a direct risk factor for autism when accounting for family-level confounders.
Population-level associations disappeared in sibling and family-based analyses, suggesting shared genetic or environmental factors drive observed links.
Key findings
01Maternal smoking in pregnancy is not a direct risk factor for autism independent of family-level factors.
02Conventional adjusted models showed an elevated risk (HR 1.17), but this association was attenuated to null in family-based models.
03Risk estimates for autism sub-phenotypes (with or without ADHD or intellectual disability) did not support a causal relationship after accounting for shared family factors.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study only examined direct maternal smoking during pregnancy and cannot be generalized to second-hand smoke, paternal smoking, or grandparental exposure. Sibling comparisons are largely driven by the small proportion of families (26% in the discordant analysis) where the mother's smoking behavior changed between pregnancies, which may introduce bias if other unmeasured factors changed simultaneously. Self-reported smoking status was collected at a single antenatal visit, though it was validated against biomarkers in a separate sample.
Declared interests
The authors declare no financial or other conflicts of interest.
The easy way to misread this
Do not conclude that smoking during pregnancy is safe for neurodevelopment. This study addresses whether it causes autism specifically when controlling for family background, not whether it harms the fetus generally. The authors explicitly state that smoking has many other deleterious health impacts.