Fetal growth restriction, low birth weight, and preterm birth: Effects of active or passive smoking evaluated by maternal expired CO at delivery, impacts of cessation at different trimesters

INTRODUCTION: The objectives of this study were to evaluate the effect of cessation of active smoking during the 1st, 2nd, and 3rd trimesters of pregnancy on the risk of reduced birth weight and prematurity using an exhaled carbon monoxide biomarker with a cut-off value ≥3 ppm as well as the effects of passive smoking. METHODS: This was a multicenter prospective cohort study involving pregnant smokers and non-smokers. Pregnant smokers were identified at the first prenatal visit before 15 weeks of amenorrhea by the number of cigarettes smoked per day and by the carbon monoxide breath test. Women were classified into 6 groups: non-smokers, passive smokers, first trimester cessation, second trimester cessation, third trimester cessation, and smoking throughout pregnancy. Smoking cessation was defined if the pregnant woman reported quitting smoking and if she achieved an exhaled CO level of <3 ppm. The association between smoking cessation and fetal growth restriction or prematurity was assessed by multivariate logistic regression. Passive smoking was defined for non-smoking women on declarative smoking status and exhaled CO ≥3 ppm. The association between passive smoking and fetal growth restriction or prematurity was assessed by multivariate logistic regression. RESULTS: The number of patients included was 5244. The incidence of fetal growth restriction below the 10th percentile was 10.6%, 12.1%, 8.5%, 9.1%, 21.1%, and 22.9%, respectively, for the non-smoking, passive smoking, first, second, third trimester cessation, and full-pregnancy smoking, groups. The risk of FGR compared to non-smokers was OR=2.3 (95% CI: 1.18–4.30, p=0.014) for patients who quit smoking in the third trimester, OR=2.5 (95% CI: 2.03–3.12, p<0.001) for women who smoked throughout pregnancy. After logistic regression, FGR (AOR=1.9; 95% CI: 0.96–3.82) for women who quit smoking in the 3rd trimester (AOR=1.8; 95% CI: 1.38–2.31, p<0.001). The risk of FGR <5th percentile was AOR=1.96 (95% CI: 1.36–2.48, p<0.001). CONCLUSIONS: Active or passive smoking during pregnancy is associated with an increased risk of intrauterine growth restriction and low birth weight. Cessation in the 1st and 2nd trimester reduces the risk of intrauterine growth restriction or low birth weight. Passive smoking has a deleterious impact on fetal development, intermediate to that of active smoking.