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, told this news organization.
“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 one in six choose to deliver by elective cesarean.”
The study was published online 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 U.K. hospitals.
At routine visits at 11-13 weeks’ gestation, 57,131 pregnancies were screened, and 1,138 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,” Dr. Magee said.