Secondhand smoke exposure and fetal loss in nonsmoking pregnant women: a meta-analysis

Background Recent meta-analyses have reported inconsistent pooled relative risks of miscarriage associated with secondhand smoke exposure. Methods We conducted a meta-analysis to examine the relationship between fetal loss and maternal secondhand smoke exposure during pregnancy in nonsmoking women. The outcome measures included spontaneous abortion and stillbirth. We searched PubMed, Web of science, Ovid and Cochrane databases up to May 1, 2026. Statistical analysis was performed using R version 4.3.1. Pooled odds ratios (ORs) with 95% confidence intervals were estimated using random-effect models. Results Our analysis included 21 studies that assessed the effects of secondhand smoke exposure in nonsmoking pregnant women. Secondhand smoke exposure significantly increased the risk of fetal loss (OR: 1.21 [95% CI: 1.11–1.31]; I2 = 55%; τ2 = 0.007; P_het < 0.01). When stratifying fetal loss into spontaneous abortion and stillbirth, secondhand smoke exposure was associated with increased risks of spontaneous abortion (OR: 1.18 [95% CI: 1.02–1.37]; I2 = 66%; τ2 = 0.010; P_het < 0.01; 10 studies) and stillbirth (OR: 1.27 [95% CI: 1.10–1.46]; I2 = 18%; τ2 = 0.006; P_het = 0.28; 10 studies). Conclusion This study provided compelling evidence that secondhand smoke exposure during pregnancy increased the risk of fetal loss, emphasizing the need for avoidance.