The effect of active and passive smoking during pregnancy on birth outcomes: A cohort study in Shanghai.

Introduction: China is the largest tobacco consumer in the world, and tobacco poses a serious threat to the health of pregnant women. However, there are relatively few domestic studies on smoking during pregnancy and childbirth outcomes among pregnant women. The purpose of this study was to analyze the effect of active and passive smoking on pregnant women and their pregnancy outcomes, providing evidence and recommendations for intervention measures.

Methods: This was a cohort study in Shanghai from April 2021 to September 2023. According to the smoking status of pregnant women, they were divided into three groups: active smokers, passive smokers and non-smokers. A self-designed questionnaire was utilized to conduct the survey, and their pregnancy outcomes were tracked and followed up.

Results: A total of 3446 pregnant women were included in this study, among which 2.1% were active smokers, 43.5% were passive smokers, and 54.4% were non-smokers. The average age of the pregnant women was 29.9 years, and 41.2% had a university degree or higher. The education level of active smokers and passive smokers was significantly lower than that of non-smokers (p<0.05).The average gestational age of non-smokers was 38.6 weeks, and the birth weight was 3283.2 g, which was higher than those of active smokers and passive smokers (p<0.05). Logistic regression analysis showed that passive smoking increased the likelihood of preterm birth (AOR=1.38; 95% CI: 1.05-1.81), low birth weight (AOR=1.53; 95% CI: 1.10-2.12), and intrauterine growth restriction (AOR=1.35; 95% CI: 1.02-1.79), while active smoking increased the likelihood of preterm birth (AOR=2.98; 95% CI: 1.50-5.90), low birth weight (AOR=4.29; 95% CI: 2.07-8.88), intrauterine growth restriction (AOR=2.70; 95% CI: 1.37-5.33) , and birth defects (AOR=2.66; 95% CI: 1.00-6.97).

Conclusions: Our findings illustrate that active and passive smoking can lead to adverse pregnancy outcomes. This study provides data on the relationship between smoking during pregnancy and delivery outcomes among pregnant women. In the future, we need more effective strategies to protect pregnant women from the harm of tobacco.