Incidence of adverse pregnancy outcomes based on the degree of short inter-pregnancy interval

To compare adverse pregnancy outcomes between patients with and without short inter-pregnancy intervals (IPI), stratified by the degree of short IPI: < 6 months, < 12 months and < 18 months. A retrospective cohort study of patients with two singleton pregnancies between 2015 and 2018 at a single academic center. The following primary outcomes were compared between patients with < 6 months, >6 and < 12 months, >12 and < 18 months, and ≥18 months IPI: hypertensive disorders of pregnancy (HDP) (gestational hypertension and preeclampsia), preterm birth (PTB) < 37 weeks, low birth weight (LWB) (< 2500g) and presence of congenital anomalies. Secondary outcomes included birthweight and gestational age at birth. Bivariate and multivariate analyses were done to examine the independent role of the degree of short IPI and each outcome. A total of 1,698 patients were included, with 103 pregnancies occurring at IPI < 6 months, 210 at IPI >6 and< 12 months, 255 at IPI >12 and < 18 months and 1,130 pregnancies at IPI ≥18 months. In bivariate analysis, patients with IPI < 6 months had the highest rate of PTB at 18.5%, followed by 8.6% PTB rate at IPI < 12 months. While the rates of HDP and LBW were higher at IPI < 6 months compared to all other groups, and the rate of congenital anomalies was the highest at IPI< 18 months, the differences did not reach statistical significance. Gestational age at birth and birthweight were significantly lower at IPI < 6 months compared to all other groups (p< 0.001 for both). In multivariate analysis, controlling for sociodemographic and clinical confounding factors, IPI < 6 months was associated with 2.11 higher odds of PTB (95% CI 1.17-3.79) and with 128g lower birthweight (95% CI -242 – -12) than IPI ≥18. In addition, IPI < 18 months was associated with higher odds of congenital anomalies (aOR1.81, 95% CI 1.03–3.17) (Table). In this single-site cohort, patients with IPI< 6 months had higher odds of PTB and lower birthweight while IPI< 18 months had higher odds of congenital anomalies compared to control group of ≥18 months.