Background Secondhand smoke (SHS) exposure during pregnancy increases the risk of infant stillbirth, congenital malformations, low birth weight and respiratory illnesses. However, little is known about the extent of SHS exposure during pregnancy. We assessed the prevalence of SHS exposure in pregnant women in low-income and middle-income countries (LMICs).

Methods We used Demographic and Health Survey data collected between 2008 and 2013 from 30 LMICs. We estimated weighted country-specific prevalence of SHS exposure among 37 427 pregnant women. We accounted for sampling weights, clustering and stratification in the sampling methods. We also explored associations between sociodemographic variables and SHS exposure in pregnant women using pairwise multinomial regression model.

Findings The prevalence of daily SHS exposure during pregnancy ranged from 6% (95% CI 5% to 7%) (Nigeria) to 73% (95% CI 62% to 81%) (Armenia) and was greater than active tobacco use in pregnancy across all countries studied. Being wealthier, maternal employment, higher education and urban households were associated with lower SHS exposure in full regression models. SHS exposure in pregnant women closely mirrors WHO Global Adult Tobacco Survey male active smoking patterns. Daily SHS exposure accounted for a greater population attributable fraction of stillbirths than active smoking, ranging from 1% of stillbirths (Nigeria) to 14% (Indonesia).

Interpretation We have demonstrated that SHS exposure during pregnancy is far more common than active smoking in LMICs, accounting for more stillbirths than active smoking. Protecting pregnant women from SHS exposure should be a key strategy to improve maternal and child health.