Interpregnancy Interval and Birth Outcomes: A Propensity Matching Study in the California Population

Jayme L Congdon,Kelli Ryckman,Jennet Arcara,Rebecca J Baer,Anu Manchikanti Gómez,Scott P Oltman,Laura Jelliffe-Pawlowski,Matthew S Pantell,Deborah Karasek,Sky K Feuer

doi:10.1007/s10995-022-03388-4

Abstract

IntroductionPrevious studies that used traditional multivariable and sibling matched analyses to investigate interpregnancy interval (IPI) and birth outcomes have reached mixed conclusions about a minimum recommended IPI, raising concerns about confounding. Our objective was to isolate the contribution of interpregnancy interval to the risk for adverse birth outcomes using propensity score matching.MethodsFor this retrospective cohort study, data were drawn from a California Department of Health Care Access and Information database with linked vital records and hospital discharge records (2007–2012). We compared short IPIs of < 6, 6–11, and 12–17 months to a referent IPI of 18–23 months using 1:1 exact propensity score matching on 13 maternal sociodemographic and clinical factors. We used logistic regression to calculate the odds of preterm birth, early-term birth, and small for gestational age (SGA).ResultsOf 144,733 women, 73.6% had IPIs < 18 months, 5.5% delivered preterm, 27.0% delivered early-term, and 6.0% had SGA infants. In the propensity matched sample (n = 83,788), odds of preterm birth were increased among women with IPI < 6 and 6–11 months (OR 1.89, 95% CI 1.71–2.0; OR 1.22, 95% CI 1.13–1.31, respectively) and not with IPI 12–17 months (OR 1.01, 95% CI 0.94–1.09); a similar pattern emerged for early-term birth. The odds of SGA were slightly elevated only for intervals < 6 months (OR 1.10, 95% CI 1.00–1.20, p < .05).DiscussionThis study demonstrates a dose response association between short IPI and adverse birth outcomes, with no increased risk beyond 12 months. Findings suggest that longer IPI recommendations may be overly proscriptive.

Highlights

Previous studies that used traditional multivariable and sibling matched analyses to investigate interpregnancy interval (IPI) and birth outcomes have reached mixed conclusions about a minimum recommended IPI, raising concerns about confounding
Using propensity score matching to address confounding, we found a dose response association between interpregnancy interval and preterm birth
Prolonging IPI may not align with individual priorities influencing pregnancy spacing decisions (Callegari et al, 2017), and delaying pregnancy may lead to decreased fertility (Schmidt et al, 2012)

Summary

Introduction

Previous studies that used traditional multivariable and sibling matched analyses to investigate interpregnancy interval (IPI) and birth outcomes have reached mixed conclusions about a minimum recommended IPI, raising concerns about confounding. Short interpregnancy interval (IPI), commonly defined as < 18 months between a livebirth and subsequent conception (Gemmill & Lindberg, 2013), may increase the risk of adverse birth outcomes such as preterm birth, (Ahrens et al, 2018; Conde-Agudelo et al, 2006; DeFranco et al, 2014), early-term birth (DeFranco et al, 2014), or small for gestational age (SGA; Ahrens et al, 2018; Conde-Agudelo et al, 2006) Evidence of this association prompted the incorporation of birth spacing recommendations into U.S clinical guidelines (American Academy of Family Physicians, 2015; Gavin et al, 2014; Louis et al, 2019) and public health objectives (US Department of Health and Human Services & Office of Disease Prevention & Health Promotion, 2010). These factors underscore the importance of clear evidence to guide public health initiatives, clinical counselling, and individual decision making

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