OBJECTIVE: This systematic review and meta-analysis aimed to evaluate the effects of electronic cigarette (E-cigarette) use and dual-use of E-cigarettes and conventional cigarettes (C-cigarettes) during pregnancy on adverse pregnancy outcomes, compared to C-cigarette use and non-use.

METHODS: A two-step search was conducted: first, systematic reviews (SRs) on the effects of E-cigarette use during pregnancy were identified from Medline and Scopus up to November 7, 2023; second, an updated search from the last search of previous SRs to May 30, 2025, was performed to capture additional relevant studies. Eligible studies included observational studies and randomized controlled trials (RCTs) that assessed the impact of E-cigarette or dual-use on adverse pregnancy outcomes, with non-use or C-cigarette use as comparators. A two-stage network meta-analysis was conducted to compare the effects of E-cigarette use, dual-use, and non-use.

RESULTS: Twelve studies (eleven observational and one RCT) were included. E-cigarette use was significantly associated with an increased risk of preterm birth (odds ratio = 1.67; 95% confidence interval [CI]: 1.11 to 2.51) and lower mean birth weight (mean difference = -57 g; 95% CI: -105 to -9) compared to non-use. However, the risks of small for gestational age (SGA), miscarriage, and mean gestational age at delivery in E-cigarette users did not differ from those in non-users. Dual use of E-cigarettes and C-cigarettes was significantly associated with increased risks of SGA, preterm birth, and lower mean birth weight compared to non-use. Compared to C-cigarette use, E-cigarette use was associated with lower risks of SGA and higher mean birth weight, while risks of preterm birth, miscarriage, and mean gestational age at delivery, did not differ between E-cigarette and C-cigarette users.

CONCLUSION: E-cigarette use during pregnancy was significantly associated with an increased risk of preterm birth and lower mean birth weight compared to non-use. Additionally dual-use was associated with elevated risks of SGA, preterm birth, and lower mean birth weight, compared to non-use. Although E-cigarette use was significantly associated with higher mean birth weight and decreased risk of SGA compared with C-cigarettes, no significant association was observed for other outcomes. These findings may be influenced by residual confounding and further high-quality studies are warranted to clarify the effect of E-cigarette use during pregnancy.

TRIAL REGISTRATION: The review protocol has been registered at the PROSPERO website since 19 March 2024 (CRD42024521271).