BACKGROUND-AIM:
E-cigarette use is increasing globally, including among women of reproductive age. Despite robust evidence that cigarette smoking negatively impacts fetal growth, data on vaping in pregnancy remain contradictory, with much of the evidence against vaping derived from registry datasets lacking biomarker-validated exposure status. The ECHO study is a large, prospective, multi-centre cohort funded by Science Foundation Ireland and Tobacco Free Ireland. It longitudinally follows pregnant women exposed to smoking, vaping or dual use, compared with non-exposed controls. This analysis presents novel data on the effect of vaping on third-trimester fetal growth.

METHODS:
Exposure status was determined using questionnaires (at screening, anatomy scan, third-trimester scan and birth) and objective biomarkers (urinary cotinine and breath CO). Third-trimester growth scans were performed at 32–34+6 weeks using Voluson E8/E10 machines. Fetal biometry and estimated fetal weight (EFW) were extracted from Viewpoint 6 and converted to gestational-age-adjusted centiles using published reference charts (Snijders 1994; Nicolaides 2018). Due to non-normal distribution, centiles were analysed using Kruskal–Wallis tests with Dunn’s post-hoc correction to compare controls, smokers, vapers and dual users.

RESULTS:
For EFW, significant group differences were observed (p=0.0067). Post-hoc testing showed reduced EFW in smokers (p<0.001) and dual users (p=0.011) compared with controls and vapers. For femur length, group differences were also significant (p=0.024), with smokers (p<0.001) and dual users (p=0.007) again demonstrating lower measurements for gestational age than controls and vapers. For abdominal circumference, overall group differences were present (p=0.039), with a trend toward reduction in smokers and dual users that did not reach statistical significance (p=0.06). Across all parameters, smoking—and to a lesser extent dual exposure—was associated with reduced fetal growth. In contrast, vaping showed no significant reduction in any biometry measure when compared with controls.

CONCLUSIONS:
This large biomarker-validated analysis demonstrates that smoking and dual exposure are associated with impaired third-trimester fetal growth, whereas vaping was not associated with significant growth restriction. These findings align with emerging prospective evidence and contrast with registry-based reports suggesting harm from vaping. While the dual-exposure subgroup was small and the analysis is limited to third-trimester growth, results suggest that vaping does not replicate the growth-limiting effects of smoking. Longitudinal follow-up will provide critical data on postnatal growth and neurocognitive outcomes at 1 and 2 years.