Effects of passive smoking on severe nausea and vomiting of pregnancy among urban Chinese nonsmoking women

Background: Nausea and vomiting of pregnancy (NVP) is one of the most common pregnancy-associated symptoms, but little is known about the effects of passive smoking on this symptom. Passive smoking among women is widespread and severe in China due to the high proportion of men who smoke actively. The aim of this study is to examine the association between maternal passive smoking and severe NVP in early pregnancy among nonsmoking women in urban China. Methods: We collected information on passive smoking status and severe NVP in early pregnancy based on an ongoing prospective cohort study conducted from October 2017 to May 2019 in Beijing, China. We used multivariable logistic model to calculate adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) after controlling for confounding factors. Results: Among 3064 participants who were involved in the final analysis, 7.4% (n = 227) were passive smokers and 9.8% (n = 299) reported severe NVP. After adjusting for potential confounders, passive smoking conferred an increased risk of NVP (adjusted OR = 1.62, 95% CI: 1.08, 2.43). The frequency of exposure to second-hand smoke showed a positive relationship with the risk of severe NVP, and significant subgroup differences were also observed in stratified analyses by parity and education level. Conclusions: Our results suggested that maternal exposure to second-hand smoke remained to be a major public health problem in urban China, and that passive smoking during the first trimester may increase the risk of severe NVP among nonsmoking pregnant women. Measures should be taken to reduce the impact of second-hand smoke exposure on pregnant women.