How parental smoking during pregnancy impacts overweight risk

September 15, 2020
Miranda Hester

Ms. Hester is Content Specialist with Contemporary OB/GYN and Contemporary Pediatrics.

Smoking has many negative health effects and a new investigation adds an increased risk of childhood weight issues when exposure to smoking in utero.

Research has shown over the past decades just how much pregnancy can impact the offspring’s life and health outcomes. Exposure to cigarette smoke has been shown to be an avoidable risk factor for birth complications and could even have an impact on the risk of a child being overweight. An investigation in PLoS Medicine further examines the association.1

The investigators ran a data meta-analysis of 28 pregnancy/birth cohorts from both North America and Europe. Every cohort included in the meta-analysis contained information on the mother’s smoking and 16 of the cohorts also had information on the father’s smoking. Additionally, 22 of the cohorts were population-based and the birth years ranged from 1991 to 2015. Across the cohorts, the maternal median age was 30.0 years and overall the mothers were either medium or highly educated.

Researchers found that when compared to nonsmoking mothers, maternal first trimester smoking only had no link to adverse birth outcomes, but was linked with an increased risk of childhood overweight (odds ratio [OR] 1.17 [95% CI 1.02–1.35], P value = 0.030). For children who had mothers that continued to smoke throughout pregnancy, there were higher risks of preterm birth (OR 1.08 [95% CI 1.02–1.15], P value = 0.012), childhood overweight (OR 1.42 [95% CI 1.35–1.48], P value < 0.001), and small size for gestational age (OR 2.15 [95% CI 2.07–2.23], P value < 0.001). The mothers who reduced the number of cigarettes smoked between the first and third trimester, but did not quit smoking, were found to still have a higher risk of small for gestation age. The corresponding risk estimates were still smaller than for women who smoked the same number of cigarettes for the duration of the pregnancy (OR 1.89 [95% CI 1.52–2.34] instead of OR 2.20 [95% CI 2.02–2.42] when reducing from 5–9 to ≤4 cigarettes/day; OR 2.79 [95% CI 2.39–3.25] and OR 1.93 [95% CI 1.46–2.57] instead of OR 2.95 [95% CI 2.75–3.15] when reducing from ≥10 to 5–9 and ≤4 cigarettes/day, respectively [P values < 0.001]). Among the mothers who didn’t smoke, paternal smoking was not linked to adverse birth outcomes, but it was linked to childhood overweight (OR 1.21 [95% CI 1.16–1.27], P value < 0.001).

The researchers concluded that mothers smoking during pregnancy was linked to a higher risk of childhood overweight than among mothers who did not smoke. Paternal smoking was also linked to an increased risk of childhood overweight, independent of maternal smoking. The researchers believe that parental smoking prevention programs should focus on urging parents to quit before or at the start of pregnancy, not during the pregnancy.


1. Philips E, Santos S, Trasande L, et al. Changes in parental smoking during pregnancy and risks of adverse birth outcomes and childhood overweight in Europe and North America: An individual participant data meta-analysis of 229,000 singleton births. PLoS Med. 2020;17(8):e1003182. doi:10.1371/journal.pmed.1003182