[Evolution of the cesarean delivery rate from 37 weeks of gestation among nulliparas or how to evaluate the external validity of a randomized North American trial about induction of labor].

OBJECTIVE

To determine the risk of caesarean delivery (CD) when an expectant management is considered for a nulliparous reaching≥37 weeks of gestation (wog).

METHODS

This is a prospective study, including all nulliparous women who delivered at≥37 wog a singleton fetus in a cephalic presentation between the first January 2017 and the 31st December 2017 in a French perinatal network (Mypa). For each week of gestation from 37 wog to 41 wog, the rate of CD was determined according the onset of labor (spontaneous or induced). The risk of CD when expectant management was considered at a specific gestational age was calculated by taking all the population who reached this gestational age, minus all women who had an induction of labor or underwent a caesarean delivery before labor.

RESULTS

In total, 16,085 women delivered at≥24 wog, and 5498 (34.1%) were nulliparous with a singleton fetus in a cephalic presentation reaching 37SA. The risk of CD increased from 40 wog, whatever the labor was spontaneous or induced (when labor was spontaneous, the risk of CD was stable till 39 wog around 11%, and increased from 14% at 40 wog to 20% at 41 wog; similarly, when labor was induced, the risk of CD was stable till 39 wog around 28%, and increased from 40% at 40 wog to 38% at 41 wog. The risk of CD for a nulliparous reaching>37 Wog when expectant management is considered was stable around 22.3%.

CONCLUSION

The risk of CD for a nulliparous reaching≥37SA when expectant management is considered is similar than the one in the United States of America.