Interpregnancy interval after vacuum delivery and subsequent perinatal outcomes.

Objective: To evaluate whether a short interpregnancy interval (IPI) after vacuum extraction (VE), poses similar perinatal risks in a subsequent pregnancy.

Methods: This was a retrospective, single-center cohort study between 2011 and 2021. Nulliparous women with term, singleton VE deliveries and with known pregnancy outcomes in their subsequent pregnancy were eligible for inclusion in the study. Each woman was allocated into one of two groups based on the IPI, <18 months and between 18 and 60 months. The primary outcome was the risk of spontaneous preterm birth (PTB) <37 weeks in the consecutive birth.

Results: We included 1094 pregnancies: 212 (19.4%) with IPI <18 months and 882 (80.6%) with IPI between 18 and 60 months following the previous VE delivery. The VE characteristics were comparable between the groups. Young maternal age was a risk factor for a short IPI (28.0 ± 4.8 vs 30.3 ± 4 years, P < 0.01). Spontaneous PTB <37 weeks was significantly higher in the IPI <18 months group with 18-60 months (7.1% vs 2.6%, P = 0.002). Polynomial regression analysis also confirmed a significantly increased risk of preterm birth <37 weeks (P < 0.01). Short IPI <18 months was also associated with an increase in the risk of low birthweight <2500 g (6.1% vs 2.8%, P = 0.02) and admission to the neonatal intensive care unit (6.1% vs 2.6%, P = 0.013). The incidence of recurrent VE, albeit significant (2.3% vs 4.9%, P = 0.049), was low in both groups. No differences were noted in any of the other secondary outcomes.

Conclusion: Short IPI (<18 months) following term VE delivery is associated with higher neonatal risks, particularly PTB, in the subsequent pregnancy. These findings are particularly important when counseling women planning an optimal IPI.