The studies compared pregnancy outcomes across 4 groups: nonsmokers, tobacco smokers, people who exclusively vaped, and dual users (smoking and vaping).

Vaping was associated with higher odds of premature birth (40%), low birth weight (49%), and being small for gestational age (32%; birth weight less than 90% of babies at the same stage of pregnancy) than not smoking.

There were no differences between tobacco smokers, people who vaped, or dual users in risk for preterm birth or low birth weight. Interestingly, the odds of an infant being small for gestational age was associated less with vaping than with smoking (47% lower) or both smoking and vaping (67% lower).

Most of the studies had a low-to-moderate risk of bias. There was also a potential publication bias.

Vaping during pregnancy may be no safer than smoking Original paper