Factors associated with short inter-pregnancy intervals in a contemporary cohort

Several studies have shown that the prevalence of short inter-pregnancy intervals (IPI), defined as < 18 months between delivery and the conception of subsequent pregnancy, varies amongst maternal demographic profiles; however these results have been inconsistent and not specific to the population in the Midwest. The objective of this study was to identify maternal demographic and clinical factors associated with short IPI. A case-control study of patients with >1 pregnancy during 2015-2018 in a single academic medical center in the Midwest. Cases were defined as patients with short IPI, described in three categories: < 6 months, > 6 months and < 12 months and >12 months and < 18 months. Controls were defined as pregnancy with IPI of ≥ 18 months. Bivariate comparisons of patients’ characteristics were conducted using chi-square and Fisher exact test for categorical data and student t-test and Wilcoxon signed-rank test for continuous measures. Multivariate logistic regression was done to identify factors independently associated with each short IPI category. A total of 1,698 patients were included in the analysis, with 568 cases of short IPI and 1,130 controls, with a rate of 33.5% of short IPIs. Patients with IPI < 6 months were more likely to be younger, self-report as non-Hispanic black, have a higher BMI, to be single, and have a public insurance (Table 1). Both IPI of < 6months and IPI of >6 and < 12 months had higher rates of prior preterm birth (p=0.018). When controlling for confounding factors in multivariable logistic regression, higher maternal age was associated with lower odds of all cases of short IPI and Hispanic ethnicity was associated with lower odds of IPI >12 and < 18 months. Public insurance status was associated with higher odds of IPI < 6 months. A history of prior preterm birth was associated with higher rates of all cases of short IPI (Table 2). In this analysis, we identified public insurance and a history of preterm birth to be independent risk factors for short inter-pregnancy intervals.View Large Image Figure ViewerDownload Hi-res image Download (PPT)