Risk of cesarean delivery in ongoing pregnancies of nulliparous women
after 37 weeks of gestation: a prospective cohort study
Abstract
Objective: To study the risk of CD for each gestational week among
ongoing pregnancies of nulliparous women at term. Design: A
retrospective, population-based cohort study from January 1, 2016,
through December 31, 2017 Setting: a French perinatal network of the
Yvelines district, France Population: 11 308 nulliparous women with a
singleton fetus in a cephalic presentation and delivered at term
(≥37-week +0 day) Methods: for each week of gestation at term, we
defined ongoing pregnancies as all pregnancies undelivered at the start
of each week. Regression models adjusted by maternal characteristics and
hospital status were used to compare the CD risk between ongoing
pregnancies and the pregnancies delivered the preceding week. The same
methods were applied to subgroups defined by the mode of labor onset.
Main outcome measure: The caesarean delivery rate (CD) Results: Ongoing
pregnancies > 40 weeks+0 days were associated with a higher
risk of CD compared with pregnancies delivered the previous week: 24.3%
in ongoing pregnancies ≥ 40 weeks +0 days versus 19.9% in deliveries
between 39 weeks +0 days and 39 weeks+6 days (Odd ratio adjusted of
1.28, 95%CI [1.15-1.44]; 30.4% in ongoing pregnancies ≥ 41 weeks
+0 days versus 19.6% in deliveries between 40 weeks +0 days and 40
weeks+6 days (OR 1.73, 95%CI [1.51-1.96]). This was also shown for
all modes of labor onset and in every maternity unit. Conclusions: CD
rates increased starting at 40 weeks +0 days in ongoing pregnancies,
regardless of the mode of labor onset.