RESUMEN
PURPOSE: WHO sets 24 months as the ideal minimum interpregnancy interval (IPI) to minimize maternal and perinatal adverse outcomes. Some studies suggest that an interval longer than 59 months may affect these outcomes, but little is known about its influence on labor. The primary objective of this study was to compare the cesarean delivery rate between primiparous women with a long IPI and, on the one hand, primiparous women with an ideal minimum IPI of 18-24 months and, on the other hand, with nulliparous women. METHODS: This retrospective cohort study of 17 years included nulliparas and primiparas who gave birth to live singleton fetuses in cephalic presentation after 22 weeks of gestation. Women with an IPI < 18 months or from 24 to 59 months were excluded, as were women with planned cesarean. We analyzed three groups: primiparous women with a long IPI defined as > 59 months, primiparous women with an ideal minimum IPI (18-24 months), and nulliparous women. RESULTS: The study included 18,503 women: 1342 women in the "long IPI" group, 1388 in the "ideal minimum IPI" group, and 15,773 in the nulliparous women group. The cesarean delivery rate was significantly higher in the long compared to the ideal minimum IPI group [12.2% vs. 6.3%, respectively; aOR = 2.2 (95% CI 1.6-3.1)], but both groups had similar durations of labor, regardless of mode of delivery. Women in the long IPI group had significantly lower cesarean rates than nulliparous women [12.2% and 14.3%, respectively; aOR = 0.5 (95% CI 0.4-0.7)], and the nulliparous women had a significantly longer mean duration of labor. CONCLUSIONS: Primiparas with a long IPI, compared with ideal minimal IPI have a higher risk of cesarean delivery during labor. Compared with nulliparous women, primiparous women with a long IPI had a lower cesarean rate.