Research from JAMA Psychiatry — Prenatal Smoking Exposure and the Risk of Psychiatric Morbidity Into Young Adulthood

Background: Reductions in maternal smoking can prevent pregnancy complications and adverse effects to foetus. Our objective was to study how the prevalence of maternal smoking differs between Nordic countries, and to identify target groups for smoking-cessation interventions. Methods: Information on maternal smoking and background factors was requested from the Nordic countries (the Danish National Board of Health, the Finnish National Institute for Health and Welfare, the Public Health Institute in Iceland, the Norwegian Institute of Public Health and the Swedish National Board of Health and Welfare). Data on maternal smoking were received from 1991 to 2010 in Denmark, 1987 to 2010 in Finland, 1999 to 2009 in Norway and 1983 to 2008 in Sweden. Trends in smoking were studied by using test for relative proportion. Results: The prevalence of maternal smoking in early pregnancy has declined in the countries during the past 20 years (Denmark: from 30.6 to 12.5%; Norway: 20.6 to 16.5% and Sweden: 31.4 to 6.9%), except in Finland (a steady prevalence at 15%). The highest rates of smoking in early pregnancy were among teenagers (24% in Sweden and 49% in Finland and Norway). Single women were 2–3 times more likely to smoke than married women. The women in the lowest socioeconomic group were 6–7 times more likely to smoke than women in the highest group in Finland and Norway. Conclusion: Maternal smoking and its trends differed between the Nordic countries. The highest smoking rates during pregnancy were observed among teenagers, single women and women with a low socioeconomic position.

Maternal smoking during pregnancy has been associated with an increased risk for psychiatric morbidity. We further studied this with Finnish siblings to control for genetic/familial factors. From the Finnish Medical Birth Register, sibling pairs were selected as the first two children born 1987–1995 to the same mother (n = 150 168 pairs), along with information on maternal smoking (no smoking/smoking). Information on the children’s psychiatric diagnoses related to outpatient care visits (1998–2013) and inpatient care (1987–2013), and the mothers’ psychiatric morbidity (1969–2013) was derived from the Finnish Hospital Discharge Register. The first pair analysis compared siblings of mothers who only smoked in the first pregnancy (Quitters, 4.7%) and mothers who smoked in both pregnancies (Smokers, 9.6%); the second analysis included mothers who smoked only in the second pregnancy (Starters, 3.3%) and mothers who did not smoke in either pregnancy (Nonsmokers, 77.5%). Smoking information was missing for 5.0% of pairs. Psychiatric morbidity of the siblings and mother was included in the statistical analyses. The risk of psychiatric diagnoses was significantly lower for the second child of quitters (adjusted OR 0.77, 95% CI 0.72–0.83) compared to the risk among smokers. A higher risk for psychiatric diagnoses was found for the second child of starters (1.39, 1.30–1.49) compared to the risk among nonsmokers. The effect of smoking was more robust for externalizing diagnoses. Maternal smoking was independently associated with a higher risk for psychiatric morbidity in children, even when controlling thoroughly for genetic and familial factors. Maternal smoking during pregnancy has an independent effect on the risk of psychiatric morbidity in children, even after controlling for non-measurable genetic/familial factors by using a sibling pair design. The effect of maternal smoking was robust for externalizing diagnoses. Maternal smoking during pregnancy had an effect on diagnoses both in outpatient and inpatient care.