Prenatal vitamin C and E supplementation in smokers is associated with reduced placental abruption and preterm birth: a secondary analysis

Objective: Smoking and pre-eclampsia (PE) are associated with increases in preterm birth, placental abruption and low birthweight. We evaluated the relationship between prenatal vitamin C and E (C/E) supplementation and perinatal outcomes by maternal self-reported smoking status focusing on outcomes known to be impacted by maternal smoking.

Design/setting/population: A secondary analysis of a multi-centre trial of vitamin C/E supplementation starting at 9-16 weeks in low-risk nulliparous women with singleton gestations.

Methods: We examined the effect of vitamin C/E by smoking status at randomisation using the Breslow-Day test for interaction.

Main outcome measures: The trial's primary outcomes were PE and a composite outcome of pregnancy-associated hypertension (PAH) with serious adverse outcomes. Perinatal outcomes included preterm birth and abruption.

Results: There were no differences in baseline characteristics within subgroups (smokers versus nonsmokers) by vitamin supplementation status. The effect of prenatal vitamin C/E on the risk of PE (P = 0.66) or PAH composite outcome (P = 0.86) did not differ by smoking status. Vitamin C/E was protective for placental abruption in smokers (relative risk [RR] 0.09; 95% CI 0.00-0.87], but not in nonsmokers (RR 0.92; 95% CI 0.52-1.62) (P = 0.01), and for preterm birth in smokers (RR 0.76; 95% CI 0.58-0.99) but not in nonsmokers (RR 1.03; 95% CI 0.90-1.17) (P = 0.046).

Conclusion: In this cohort of women, smoking was not associated with a reduction in PE or the composite outcome of PAH. Vitamin C/E supplementation appears to be associated with a reduction in placental abruption and preterm birth among smokers.