In Induction of Labor

A Medscape article reporting on a randomized controlled trial claims that induction with an unfavorable cervix doesn’t increase cesarean rates, but let’s look closer.

Investigators randomly allocated 162 1st-time mothers with a Bishop score of 5 or less (a 1-10 scale measuring cervical readiness for labor) to elective induction at 40 wk or expectant management. The cesarean rate was 31% (25/82) in the induced group vs. 18% (14/79) in the expectant management group, a difference that fell just short of achieving statistical significance, meaning that the difference may have been due to chance.

Consider this, though: trial investigators calculated how many participants would be needed to have an 80% probability of showing a doubling of cesarean rates (power calculation) from 20% to 40%. That’s a hefty increase. A smaller one, such as the 70% increase the trial actually found, would still have an important clinical impact–in this case 13 more women per 100–where baseline cesarean rates are so high but would have required more participants to reliably detect an effect.

Furthermore, more than half the “expectantly managed” women were induced (56%). This would mask any effect of induction, although expectantly managed women were at an advantage if they were induced. According to the study, they were less likely to have an unfavorable cervix at hospital admission (mean Bishop score 7.4 vs. 4.6), which would have increased their odds of induction success. Even so, one wonders what the cesarean rate would have been if, say, 90% of the expectantly managed population had been allowed to begin labor on their own.

Also important to note, all women being induced with an unripe cervix had treatment to ripen it (balloon catheter or misoprostol), which failed to close the cesarean rate gap.

The Take-Away: Quite the opposite from what the trial report claims, 1st-time mothers with an unfavorable cervix would be wise to refuse induction for other than medical indications.

 

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