Short interpregnancy interval increases the risk of preterm premature rupture of membranes and early delivery

Abstract

Objectives: Preterm premature rupture of membranes (PPROM) is a major contributor to overall preterm birth (PTB) rates. A short interpregnancy interval (IPI) is a well-known risk factor for PTB. It is unknown if a short IPI specifically affects the risk of developing PPROM in a subsequent pregnancy. We sought to determine the association between IPI and the risk of PPROM in a subsequent pregnancy.

Methods: A retrospective cohort study using the Missouri birth certificate database of singleton births from 2003 to 2013 was conducted. A short IPI (delivery of the prior pregnancy to conception of the index pregnancy) was defined as ≤6 months. IPI >6 months was categorized into two groups: IPI 7-23 months and IPI ≥24 months. PPROM was defined as premature rupture of membranes between 16⁰ and 36⁶ weeks. Multivariable logistic regression was conducted to determine the association between IPI and PPROM while controlling for maternal age, race, body mass index (BMI), education level, use of social services (Medicaid insurance, food stamps, or participation in the WIC [Women, Infants, and Children] program), tobacco use, and history of PTB. Secondary outcome included the gestational age at delivery, categorized into five subgroups (≤24⁰, 24¹-28⁰, 28¹-32⁰, 32¹-34⁰, and 34¹-36⁶ weeks).

Results: 474,957 subjects with singleton gestations had data available to calculate the IPI. Of these, 1.4% (n = 6797) experienced PPROM. IPI ≤6 months was significantly associated with an increased risk of developing PPROM compared with patients with IPI ≥24 months (odds ratio (OR) 1.80, 95% CI 1.70-1.90, p < .001). A higher proportion of women with IPI ≤6 months delivered between 28¹ and 32⁰ weeks compared to the other two IPI groups (27.0 versus 15.0 and 16.4%, p < .001). Individual maternal factors associated with an increased risk of PPROM included advanced maternal age, African American race, BMI <18.5 kg/m², BMI ≥30 kg/m², use of social services, tobacco use, and a prior PTB.

Conclusion: Our data demonstrate that an IPI of ≤6 months is significantly associated with an increased risk of developing PPROM in the subsequent pregnancy. Of greater clinical relevance is that these women were more likely to deliver between 28¹ and 32⁰ weeks as compared with women with a longer IPI. Novel to this study is the establishment of a specific link between a short IPI and PPROM with subsequent early delivery. Several maternal demographic factors known to be associated with PTB risk were also found to be associated with an increased risk of PPROM. Further studies are necessary to elucidate plausible biologic mechanisms ultimately leading to the development and implementation of preventive and therapeutic strategies for this high-risk cohort.

Keywords: Interpregnancy interval; preterm birth; preterm premature rupture of membranes.