Exposure-response analysis of the association of maternal smoking and use of electronic cigarettes (vaping) in relation to preterm birth and small-for-gestational-age in a national US sample, 2016-2018

We aimed to estimate exposure-response associations between smoking or vaping, and preterm and small-for-gestational age (SGA) births. We included 99,201 mothers who delivered live singletons in 2016-2018 from the Pregnancy Risk Assessment Monitoring System. We created exposure categories based on participants' self-reported average number of cigarettes smoked per day and vaping frequency. Dual users in late pregnancy were a heterogeneous group: 36% heavily smoked and occasionally vaped; 29% lightly smoked and frequently vaped; 19% lightly smoked and frequently vaped; and 15% both heavily smoked and frequently vaped. While dual users who heavily smoked and occasionally vaped had the highest adjusted OR for SGA (3.4, 95% CI 1.7-6.6), all the dual users were on average at about twice the odds of having SGA than non-users. While the risks of preterm birth were higher among sole light smokers (adjusted OR 1.3, 95% CI 1.1-1.5) and sole heavy smokers (adjusted OR 1.4. 95 CI 1.2-1.8) than non-users, the adjusted odds of preterm births for dual users were not noticeably higher than those of non-users, unless they were also heavy smokers. Excess of preterm births among heavy vapers was suggested. Among younger non-Hispanic white women (where vaping is most common), only excess risk of SGA, not preterm, with vaping was apparent. Relative to non-users, both smoking and vaping during pregnancy appear to increase risk of SGA, but excess risk of preterm births appears to be primarily attributable to smoking alone. Higher levels of exposure tended to confer more risk.