Determining optimal timing of birth for women with chronic or gestational hypertension at term: The WILL (When to Induce Labour to Limit risk in pregnancy hypertension) randomised trial.

Background: Chronic or gestational hypertension complicates approximately 7% of pregnancies, half of which reach 37 weeks' gestation. Early term birth (at 37 to 38 weeks) may reduce maternal complications, cesareans, stillbirths, and costs but may increase neonatal morbidity. In the WILL Trial (When to Induce Labour to Limit risk in pregnancy hypertension), we aimed to establish optimal timing of birth for women with chronic or gestational hypertension who reach term and remain well. Methods and findings: This 50-centre, open-label, randomised trial in the United Kingdom included an economic analysis. WILL randomised women with chronic or gestational hypertension at 36 to 37 weeks and a singleton fetus, and who provided documented informed consent to "Planned early term birth at 38^+0–3 weeks" (intervention) or "usual care at term" (control). The coprimary outcomes were "poor maternal outcome" (composite of severe hypertension, maternal death, or maternal morbidity; superiority hypothesis) and "neonatal care unit admission for ≥4 hours" (noninferiority hypothesis). The key secondary was cesarean. Follow-up was to 6 weeks postpartum. The planned sample size was 540/group. Analysis was by intention-to-treat. A total of 403 participants (37.3% of target) were randomised to the intervention (n = 201) or control group (n = 202), from 3 June 2019 to 19 December 2022, when the funder stopped the trial for delayed recruitment. In the intervention (versus control) group, losses to follow-up were 18/201 (9%) versus 15/202 (7%). In each group, maternal age was about 30 years, about one-fifth of women were from ethnic minorities, over half had obesity, approximately half had chronic hypertension, and most were on antihypertensives with normal blood pressure. In the intervention (versus control) group, birth was a median of 0.9 weeks earlier (38.4 [38.3 to 38.6] versus 39.3 [38.7 to 39.9] weeks). There was no evidence of a difference in "poor maternal outcome" (27/201 [13%] versus 24/202 [12%], respectively; adjusted risk ratio [aRR] 1.16, 95% confidence interval [CI] 0.72 to 1.87). For "neonatal care unit admission for ≥4 hours," the intervention was considered noninferior to the control as the adjusted risk difference (aRD) 95% CI upper bound did not cross the 8% prespecified noninferiority margin (14/201 [7%] versus 14/202 [7%], respectively; aRD 0.003, 95% CI −0.05 to +0.06), although event rates were lower-than-estimated. The intervention (versus control) was associated with no difference in cesarean (58/201 [29%] versus 72/202 [36%], respectively; aRR 0.81, 95% CI 0.61 to 1.08. There were no serious adverse events. Limitations include our smaller-than-planned sample size, and lower-than-anticipated event rates, so the findings may not be generalisable to where hypertension is not treated with antihypertensive therapy. Conclusions: In this study, we observed that most women with chronic or gestational hypertension required labour induction, and planned birth at 38^+0–3 weeks (versus usual care) resulted in birth an average of 6 days earlier, and no differences in poor maternal outcome or neonatal morbidity. Our findings provide reassurance about planned birth at 38^+0–3 weeks as a clinical option for these women. Trial registration: isrctn.com ISRCTN77258279. Laura Magee and colleagues evaluate the optimal timing of birth for women with chronic or gestational hypertension at term, in a multicentre open-label randomised trial. Author summary: Why was this study done?: Approximately 7 in 100 women have high blood pressure that developed before pregnancy (chronic hypertension) or develops during pregnancy (gestational hypertension). Chronic or gestational hypertension may lead to more serious problems for women and babies, which is particularly common near the woman's due date. It may be possible to avoid such problems by timing birth a little earlier than the due date, as long as this does not create other problems for babies. What did the researchers do and find?: In 50 hospitals in the United Kingdom, 403 (of a planned 1,080) women were recruited who had chronic or gestational hypertension, were otherwise well, and were nearing their due date. Women had an equal chance of being offered "Planned early term birth at 38^+0–3 weeks" (intervention, 201 women) or "usual care at term" (control, 202 women) until December 2022 when the funder stopped the trial for delayed recruitment. Women in the intervention (compared with the control) group, gave birth 0.9 weeks earlier (at 38.4 weeks), and there was no evidence of a difference in "poor maternal outcome" (13% versus 12%, respectively) or "neonatal care unit admission for ≥4 hours" (7% versus 7%, respectively). The intervention (versus control) was not associated with a difference in cesarean birth (29% versus 36%, respectively). What do these findings mean?: Planned early term birth at 38^+0–3 weeks may be the best option for women with chronic or gestational hypertension who are nearing their due date and remain well. While our findings are limited by a smaller-than-planned sample size, we were able to rule out differences in "poor maternal outcome" and "neonatal care unit admission for ≥4 hours" that we specified as important before the trial. While it is possible that planned early term birth may reduce the occurrence of cesarean birth, further data will be required to confirm this. [ABSTRACT FROM AUTHOR]