Objectives Short interpregnancy intervals (IPI) have been linked to multiple adverse maternal and neonatal outcomes, but less is known about prolonged IPI, including its relationship with labor progression. The objective of the study was to investigate whether prolonged IPIs are associated with longer second stages of labor. Methods A perinatal database from Kaiser Permanente Hawaii was used to identify 442 women with a prolonged IPI ≥60 months. Four hundred forty two nulliparous and 442 multiparous women with an IPI 18-59 months were selected as comparison groups. The primary outcome was second stage of labor duration. Perinatal outcomes were compared between these groups. Results The median (IQR) second stage of labor duration was 76 (38-141) min in nulliparous women, 15 (9-28) min in multiparous women, and 18 (10-38) min in women with a prolonged IPI (p<0.0001). Pairwise comparisons revealed significantly different second stage duration in the nulliparous group compared to both the multiparous and prolonged IPI groups, but no difference between the multiparous and prolonged IPI groups. There was a significant association with the length of the IPI; median duration 30 (12-61) min for IPI ≥120 months vs. 15 (9-27) min for IPI 18-59 months and 16 (9-31) min for IPI 60-119 months (p=0.0014). Conclusions The second stage of labor did not differ in women with a prolonged IPI compared to normal multiparous women. Women with an IPI ≥120 months had a significantly longer second stage vs. those with a shorter IPI. These findings provide a better understanding of labor progression in pregnancies with a prolonged IPI.
Keywords: IPI; interpregnancy interval; labor progression; multiparous women; pregnancy spacing; prolonged interpregnancy interval; second stage of labor.