Objective: To study the outcomes of extremely preterm infants of hypertensive mothers who smoke.
Study design: This retrospective cohort study included infants born between 2003 and 2012 at <29 weeks' gestation and admitted to neonatal intensive care units participating in the Canadian Neonatal Network. Infants were divided into four mutually exclusive groups. Infants of hypertensive mothers who smoked; infants of hypertensive, non-smoking mothers; infants of normotensive mothers who smoked; and infants of normotensive, non-smoking mothers. Using infants of normotensive, non-smoking mothers as the reference group, neonatal outcomes were compared between the groups. Adjusted odds ratios (AORs) and 95% confidence intervals (CIs) were calculated using univariate and multivariate regression analysis.
Results: Of the 12,307 eligible infants, 172 had hypertensive mothers who smoked, 1689 had hypertensive non-smoking mothers, 1535 had normotensive mothers who smoked, and 8911 had normotensive non-smoking mothers. Compared to infants of normotensive non-smoking mothers, infants of hypertensive mothers, regardless of smoking status, had higher odds of developing bronchopulmonary dysplasia (AORs of smokers 1.62; 95% CI 1.12-2.35 and of non-smokers 1.43; 95% CI 1.24-1.64). There was no difference in the odds of mortality and retinopathy of prematurity stage ≥3 between the groups. Infants of hypertensive, non-smoking mothers had decreased odds of intraventricular hemorrhage >grade 2 and higher odds of necrotizing enterocolitis. There was decreased odds of hypertension if the mother was a smoker (AOR 0.71; 95% CI 0.59-0.85).
Conclusion: Maternal hypertension is associated with increased rates of bronchopulmonary dysplasia, irrespective of smoking status.