Timing of birth to improve outcomes in chronic or gestational hypertension: the WILL RCT

For women with chronic or gestational hypertension who remain well, early term birth (at 37-38 weeks' gestation) may reduce maternal complications, caesareans and stillbirths, but it may increase neonatal morbidity compared with expectant care. Expectant care may increase costs. There are no high-quality data to guide care, which currently involves maternal-fetal surveillance and intervention for maternal or fetal compromise, which may be rapid or unexpected.

To investigate optimal timing of birth for women with chronic or gestational hypertension who reach term and remain well.

Pragmatic, unmasked, multicentre randomised trial with a health economic analysis.

Fifty United Kingdom hospitals.

Inclusion: maternal age ≥ 16 years, chronic or gestational hypertension, singleton pregnancy, live fetus, 36⁺⁰-37⁺⁶ weeks' gestation and able to give documented informed consent. Exclusion: contraindication to either trial arm (e.g. pre-eclampsia), blood pressure ≥ 160/110 mmHg until controlled, major fetal anomaly anticipated to require neonatal care unit admission or participation in another timed birth trial.

Planned early term birth at 38^+0-3 weeks' (intervention) or 'usual care at term' (control, revised from 'expectant care until at least 40⁺⁰ weeks', August 2022).

Maternal coprimary: composite of 'poor maternal outcome' (severe hypertension, maternal death or maternal morbidity and superiority hypothesis). Neonatal coprimary: neonatal care unit admission ≥ 4 hours (non-inferiority hypothesis). Each coprimary is measured until primary hospital discharge or 28 days post birth (whichever is earlier). Key secondary: caesarean birth.

1 : 1 ratio, minimised for key prognostic variables: site, hypertension type and prior caesarean.

It was not possible to mask care providers or participants to the intervention. For the coprimary maternal outcome, there was local site principal investigator/delegate sign-off based on review, masked to allocated group, of primary case notes.

From 2019 to 2022, 403 participants were randomised (37% of target 1080) to intervention (n = 201) or control (n = 202). The funder stopped the trial during the coronavirus disease discovered in 2019 pandemic for delayed recruitment. In the intervention (vs. control) group, birth was a median of 0.9 weeks earlier (38.4, interquartile range 38.3-38.6 vs. 39.3, interquartile range 38.7-39.9 weeks). There was no evidence of a difference in 'poor maternal outcome' (13% vs. 12%, respectively; adjusted risk ratio 1.16, 95% confidence interval 0.72 to 1.87). For 'neonatal care unit admission ≥ 4 hours', the intervention was considered to be non-inferior to control, as the adjusted risk difference, 95% confidence interval upper bound did not cross the 8% pre-specified non-inferiority margin (7% vs. 7%, respectively; adjusted risk difference 0.003, 95% confidence interval -0.05 to +0.06), although event rates were lower than estimated. There was no evidence of a difference in caesarean (29% vs. 36%, respectively; adjusted risk ratio 0.81, 95% confidence interval 0.61 to 1.08).

Recruitment was 37% of the anticipated sample size (as above).

Despite being unable to recruit to target in this study, we observed that most women with chronic or gestational hypertension required labour induction and planned birth at 38^0-3 weeks (vs. usual care), which resulted in birth an average of 6 days earlier and there were 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.

An individual participant data meta-analysis is planned to address whether the intervention (vs. control) reduces caesarean; low adverse event rates would make unfeasible mounting another randomised trial.

This synopsis presents independent research funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme as award number 16/167/123.