Does an unfavorable cervix preclude induction of labor at term in women who have gestational hypertension or mild preeclampsia?

The optimal management of gestational hypertension and mild preeclampsia at term has been a subject of great debate over the past decade. The controversy centers on the timing of delivery—induction of labor versus expectant management.

Proponents of immediate induction raise the valid concern that maternal disease may worsen if pregnancy is allowed to continue. Conversely, proponents of expectant management point to the possibility that the rate of cesarean delivery will be increased with immediate induction; they also cite concerns that neonatal morbidity may be increased with an early term delivery.

To shed light on this debate, investigators in the well-known HYPITAT trial randomly assigned 756 women who had gestational hypertension or mild preeclampsia at term to induction of labor (n = 377) or expectant management (n = 379). All women were carrying a singleton fetus that was 36 to 41 weeks old, with cephalic presentation. The main findings of the trial, published in Lancet, were that induction of labor produced fewer “high-risk situations” (relative risk [RR], 0.71; 95% confidence interval [CI], 0.59–0.86), with no increase in the risk of cesarean delivery (RR, 0.75; 95% CI, 0.55–1.04) or adverse neonatal outcomes (RR, 0.75; 95% CI, 0.45–1.26).¹

Although these findings are important, one question lingered in the minds of many obstetricians: Should the choice between induction of labor and expectant management hinge on the favorability of the cervix?

That is the question addressed by Tajik and colleagues.

Zooming in on cervical status

In their secondary analysis from the HYPITAT trial, Tajik and colleagues reanalyzed the association between induction of labor and expectant management, focusing on the same outcomes (high-risk situations, cesarean delivery, adverse neonatal outcomes), but they stratified their data by cervical status. As stated above, their findings are surprising and seemingly counterintuitive:

• Among women who underwent immediate induction of labor, cervical length was not associated with a higher probability of high-risk situations
• The beneficial effect of induction of labor—in terms of reducing the rate of cesarean delivery—was greater among women who had an unfavorable cervix.

Strengths and limitations of the trial

Overall, this was a well-conducted secondary analysis that tackled an important issue. It featured 1) a robust dataset, with all variables of interest collected, and 2) a thoughtful approach to data analysis.

However, the analysis also raises a question: Is it possible that some of its negative findings (composite neonatal morbidity) are due to insufficient power? This is a question I ask whenever I encounter a secondary analysis of a randomized, controlled trial. The answer here: Possibly.

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