Beyond birth outcomes: Interpregnancy interval and injury-related infant mortality

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Paediatric and Perinatal Epidemiology


birth spacing, infant mortality, injury, interpregnancy interval, parity


Background: Several studies have examined the association between IPI and birth outcomes, but few have explored the association between interpregnancy interval (IPI) and postnatal outcomes.

Objective: We examined the association between IPI and injury-related infant mortality, a leading cause of postneonatal mortality.

Methods: We used 2011-2015 US period-linked birth-infant death vital statistics data to generate a multiyear birth cohort of non-first-born singleton births (N = 9 782 029). IPI was defined as the number of months between a live birth and the start of the pregnancy leading to the next live birth. Causes of death in the first year of life were identified using ICD-10 codes. Hazard ratios (HR) for IPI categories were estimated using Cox proportional hazards models adjusted for birth order, county poverty level, and maternal characteristics (marital status, race/ethnicity, education, age at previous birth).

Results: After adjustment, overall infant mortality (48.1 per 10 000 births) was higher for short and long IPIs compared with IPI 18-23 months (reference):
Conclusion: Unlike overall infant mortality, injury-related infant mortality decreased with IPI length. While injury-related deaths are rare, these patterns suggest that the timing between births may be a marker of risk for fatal infant injuries. The first year postpartum may be an ideal time for the delivery of evidence-based injury prevention programmes as well as family planning services.


Funding information: This work was performed under a subcontract with Atlas Research, LLC for US Department of Health and Human Services, Office of Population Affairs (HHSP‐233201450040A). Atlas Research, LLC had no role in the collection, analysis, or interpretation of the data. The role of co‐authors from the Office of Population Affairs is specified below. Federal employees performed this work under the employment of the US federal government and did not receive any outside funding. We also gratefully acknowledge support from the Eunice Kennedy Shriver National Center for Child Health and Human Development grant P2C‐HD041041, Maryland Population Research Center.