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Abstract
Introduction: Preterm birth (PTB), gestational age of < 37 weeks, is a leading cause of infant mortality across the globe. There are multiple risk factors associated with PTB but one approach to reducing PTB risk is birth spacing of 24 months or more between pregnancies. The interval between pregnancies is known as interpregnancy intervals (IPI). An IPI of less than 24 months increases the risk for preterm births. Few studies have studied the factors associated with short, appropriate, or optimal IPI. Furthermore, recent studies suggest that previous pregnancy outcomes may be related to IPI and the optimal IPI may be shorter following an early pregnancy loss than for a previous livebirth. The purpose of this study is to 1) examine the gaps in knowledge for IPIs, 2) assess the determinants of short IPIs, and 3) determine the optimal IPI window for different previous pregnancy outcomes.
Methods: We first conducted a systematic review of the literature to evaluate gaps in knowledge gaps about IPI and pregnancy outcomes. We also analyzed the INTERBIO-21st Fetal and Neonatal Study data to study IPI determinants and estimate optimal IPI based on previous pregnancy outcomes. The INTERBIO-21st studies allowed for the evaluation of IPI in an multinational setting due to the standardized methods of measurement of gestational age. To identify potential determinants of IPIs, we used descriptive statistics and bivariate analysis. We identified optimal IPIs using restricted cubic spline regression across months for women with different previous pregnancy outcomes. We used Poisson regression with robust standard errors to evaluate the associations of selected interpregnancy windows to the risk of preterm birth.
Results: Previous pregnancy history was a major predictor of short IPI. The selected IPIs for women with a previous preterm and term birth were not associated with preterm birth. However, an IPI of less than nine months was protective against the risk of preterm birth when the previous pregnancy resulted in an early pregnancy loss.
Methods: We first conducted a systematic review of the literature to evaluate gaps in knowledge gaps about IPI and pregnancy outcomes. We also analyzed the INTERBIO-21st Fetal and Neonatal Study data to study IPI determinants and estimate optimal IPI based on previous pregnancy outcomes. The INTERBIO-21st studies allowed for the evaluation of IPI in an multinational setting due to the standardized methods of measurement of gestational age. To identify potential determinants of IPIs, we used descriptive statistics and bivariate analysis. We identified optimal IPIs using restricted cubic spline regression across months for women with different previous pregnancy outcomes. We used Poisson regression with robust standard errors to evaluate the associations of selected interpregnancy windows to the risk of preterm birth.
Results: Previous pregnancy history was a major predictor of short IPI. The selected IPIs for women with a previous preterm and term birth were not associated with preterm birth. However, an IPI of less than nine months was protective against the risk of preterm birth when the previous pregnancy resulted in an early pregnancy loss.