Timing of Delivery in Women With Chronic Hypertension

OBJECTIVE: To assess whether routine induction of labor at 38 or 39 weeks in women with chronic hypertension is associated with the risk of superimposed preeclampsia or cesarean delivery. METHODS: We conducted a retrospective population-based study of women with chronic hypertension who had a singleton hospital birth at 38 0/7 weeks of gestation of gestation in Ontario, Canada, between 2012 and 2016. Women who underwent induction of labor at 38 0/7 to 38 6/7 weeks of gestation for chronic hypertension (n=281) were compared with those who were managed expectantly during that week and remained undelivered at 39 0/7 weeks of gestation (n=1,606). Separately, women who underwent induction of labor at 39 0/7 to 39 6/7 weeks of gestation for chronic hypertension (n=259) were compared with women who remained undelivered at 40 0/7 weeks of gestation (n=801). RESULTS: Of 534,529 women gave birth during the study period, 6,054 (1.1%) had chronic hypertension and 2,420 met the inclusion criteria. Women managed expectantly at 38 or 39 weeks of gestation were at risk of new-onset superimposed preeclampsia (19.2% [308/1,606] and 19.0% [152/801], respectively) and eclampsia (0.6% [10/1,606] and 0.7% [6/801], respectively), and more than half underwent induction of labor later in gestation (56.8% and 57.8%, respectively). The risk of cesarean delivery in the induction groups was lower (38 weeks of gestation) or similar (39 weeks of gestation) to that observed in women managed expectantly at the corresponding weeks (38 weeks of gestation: 17.1% vs 24.0%, adjusted relative risk 0.74 [95% CI 0.57-0.95]; 39 weeks of gestation: 20.1% vs 26.0%, adjusted relative risk 0.90 [95% CI 0.69-1.17]). CONCLUSION: Our findings suggest that in women with isolated chronic hypertension, induction of labor at 38 or 39 weeks of gestation may prevent severe hypertensive complications without increasing the risk of cesarean delivery.