Factors Associated with Secondhand Smoke Exposure Among Pregnant Women in Darkhan-Uul Province, Mongolia: A Prospective Observational Study

This prospective observational study investigated secondhand smoke (SHS) exposure levels across gestational stages and identified longitudinal associated factors among pregnant women in Darkhan-Uul Province, Mongolia. Participants recruited between October 2019 and September 2020 answered a self-administered questionnaire and provided spot urine samples at each trimester. SHS exposure was assessed via urinary cotinine (UC) levels, and generalized estimating equations were used to identify associated factors. The final sample included 526 participants. UC levels ≥ 5 ng/mL were observed in 40.1%, 32.0%, and 29.0% of participants in the first, second, and third trimesters, respectively. Compared to the first trimester, the risk of SHS exposure was significantly lower in the second (adjusted odds ratio [AOR]: 0.70; 95% confidence interval [CI]: 0.54–0.91) and third trimesters (AOR: 0.59; 95% CI: 0.45–0.77). Additionally, compared to smoke-free households, those permitting smoking in designated areas (AOR: 1.70; 95% CI: 1.28–2.26) or having no restrictions (AOR: 2.54; 95% CI: 1.29–4.96) showed higher odds of exposure. These results highlight the importance of household smoking restrictions and should be disseminated among pregnant women, their families, and healthcare providers to reduce risk of SHS exposure.