BACKGROUND-AIM:
E-cigarette use is increasingly common in pregnancy, yet its effects on maternal and infant outcomes remain unclear due to limited high-quality longitudinal studies. International recommendations conflict: the UK considers e-cigarettes a cessation aid, whereas the US Surgeon General discourages their use. While registry studies suggest vaping increases the risk of small-for-gestational-age (SGA) infants, several prospective studies, including a pilot from our institution, have not found birthweight differences. Robust evaluation of vaping in pregnancy is needed to guide clinical advice.

METHODS:
This prospective, multi-centre, observational cohort study is registered with NCT: 06297005. The study protocol has been published. Four groups of pregnant women were recruited; smokers, e-cigarette users, dual users and non-users (controls). Their exposure status was objectively assessed using specific biomarkers - breath carbon monoxide and urine cotinine assays. A targeted fetal ultrasound in the third trimester gathered data on fetal growth parameters. Obstetric outcomes examined included birthweight, small for gestational age, low birth weight and gestational age at delivery.

RESULTS:
We recruited 726 women, for whom primary outcomes were available for 684. Demographic details were broadly similar across groups with the exception of dual-users who were significantly younger than other groups (p-value <0.05). Vaping mothers had infants of similar birthweight to controls (p-value 0.8) and their babies were significantly heavier than those of smoking mothers (p=0.05). Smokers had significantly more babies < 10th percentile for gestational age than vapers (p-value <0.0001). We found no significant difference in median gestational age at delivery; the rate of preterm birth or admission to NICU, however, numbers with these outcomes were low. A multiple regression analysis of birthweights adjusting for age, BMI, parity and gestational age at delivery was completed. Smokers had lower birthweight weights (adjusted mean=3155g), compared to controls (3369g; p<0.001), vapers (3368; p<0.001) and dual vaper/smokers (3247g; p=0.454). This is consistent with the univariate analysis and suggests that, after adjusting for important prognostic variables, birthweights for vapers are very similar to those of non-smokers.

CONCLUSIONS:
Unlike cigarette smoking, e-cigarette usage in pregnancy is not associated with an increase in small for gestational age babies. This is a clinically relevant finding and contrasts with earlier studies which interpret large datasets. The strength of our study lies in its prospective design and use of objective biomarker determination of exposure groups providing reliable confirmation of cigarette consumption and e-cigarette usage. We await the findings of the subsequent paediatric analyses of this study which will examine growth and neurocognitive outcomes in the infant participants at 6 months, 1 and 2 years of age.