At-Term Birth Timing May Cut Preeclampsia
Risk in Half

Marilynn Larkin

April 13, 2023

Risk-stratified timing of birth at term may reduce a mother's risk of preeclampsia by half, analysis of a large UK cohort suggests.

Timed birth strategies include scheduled labor inductions and cesarean deliveries.

In this observational analysis of nearly 90,000 pregnancies, at-term preeclampsia occurred with similar frequency among women routinely screened during the first trimester and among at-risk women screened during the third trimester.

Overall, on average, at-risk women delivered at 40 weeks, with two thirds experiencing spontaneous onset of labor. About one fourth had cesarean deliveries.

"We anticipated that timed birth at 37 weeks could reduce the occurrence of more than half of preeclampsia, [but] this is not an intervention that could be recommended, as complications for the baby would be increased," Laura A. Magee, MD, of King’s College London, United Kingdom, told | Medscape Cardiology.

"However, we were delighted to see that a personalized approach to timed birth, based on an individual woman's risk of preeclampsia, could prevent a similar number of cases of preeclampsia, with fewer women requiring timed birth and at later gestational ages, when newborn problems would be less frequent."

Although not currently recommended to prevent at-term preeclampsia, "timed birth by labor induction is a very common timing of birth strategy," she noted. "At least one third of women currently undergo labor induction at term gestational age, and 1 in 6 choose to deliver by elective cesarean."

The study was published online April 10 in the journal Hypertension.

Screening at 35-36 Weeks Superior

The investigators analyzed data from a nonintervention cohort study of singleton pregnancies delivering at ≥ 24 weeks, without major anomalies, at two UK hospitals.

At routine visits at 11 to 13 weeks' gestation, 57,131 pregnancies were screened, and 1138 term preeclampsia cases developed.

Most of these women were in their early 30s, self-identified as White and had a BMI at the upper limits of normal. About 10% were smokers; fewer than 3% had a medical history of high blood pressure, type 2 diabetes, or autoimmune disease; and 3.9% reported a family history of preeclampsia.

At 35-36 weeks, in a different cohort, 29,035 pregnancies were screened and term preeclampsia developed in 619 women. Demographics and pregnancy characteristics were similar to those screened at 11-13 weeks, although the average BMI was higher — in the overweight range — and there were fewer Black women, although they still made up 10% of the screened population.

Patient-specific preeclampsia risks were determined by the United Kingdom National Institute for Health and Care Excellence (NICE) guidance, and the Fetal Medicine Foundation competing-risks model, available through an online calculator.

Timing of birth for term preeclampsia prevention was evaluated at 37, 38, 39, and 40 weeks or depending on preeclampsia risk by the competing-risks model at 35-36 weeks.

The primary outcomes were the proportion of term preeclampsia prevented, and number-needed-to-deliver to prevent one term preeclampsia case.

The investigators found that overall, the proportion of term preeclampsia prevented was highest, and number-needed-to-deliver lowest, for preeclampsia screening at 35-36 weeks rather than at 11-13 weeks.

For delivery at 37 weeks, fewer cases of preeclampsia were prevented with NICE criteria (28.8%) than with the competing-risks model (59.8%), and the number-needed-to-deliver was higher (16.4 vs 6.9, respectively).

At 35-36 weeks, the risk-stratified approach had similar preeclampsia prevention (57.2%) and number-needed-to-deliver (8.4), but fewer women would be induced at 37 weeks (1.2% vs 8.8%).

Although personalized timed birth at term may be an effective way to address at-term preeclampsia, "clinicians should wait for definitive clinical trial evidence," Magee said.

"Stay Tuned"

Vesna D. Garovic, MD, PhD, Mayo Clinic, Rochester, Minnesota, and chair of the 2021 AHA Scientific Statement, "Hypertension in Pregnancy: Diagnosis, Blood Pressure Goals, and Pharmacotherapy," agrees.

The new data "set the stage for adequately designed and powered studies that will provide ultimate response/evidence regarding the efficacy of this approach," she told | Medscape Cardiology.

"Future studies need to address the safety of this approach," she added, "as close to 10 timed/planned deliveries will be needed to prevent one case of preeclampsia."

For now, she said, "While these preliminary data are promising, they are not sufficient to adopt timed birth in daily practice. Prospective studies that will provide sufficient evidence regarding the efficacy and safety of this approach are likely to follow. Stay tuned."

Indeed, Magee noted that the Fetal Medicine Foundation is about to launch a randomized trial of a personalized 'timing of birth' strategy at term based on the preeclampsia risk described in her group’s study vs usual care at term — that is, "watchful waiting, and delivery should preeclampsia or another indication for birth develop."

The study was supported by grants from the Fetal Medicine Foundation, UK, and various biotech companies provided reagents and relevant equipment free of charge. Magee and Garovic reported no relevant financial relationships.

Hypertension. Published online April 10, 2023. Full text

Follow Marilynn Larkin on Twitter:  @MarilynnL.

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