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Updated: Mar 18, 2026

Modeling Ascending Vaginal Infection, Preterm Birth, and Neonatal Morbidity in Mice
Published on: October 10, 2025
Interpregnancy interval after live birth or pregnancy termination and estimated risk of preterm birth: a
B Z Shachar1, J A Mayo2, D J Lyell3
1Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA. bettyshachar@gmail.com, bshachar@stanford.edu.
Objectives:
We assessed whether interpregnancy interval (IPI) length after live birth and after pregnancy termination was associated with preterm birth (PTB).
Design:
Multiyear birth cohort.
Settings:
Fetal death, birth and infant death certificates in California merged with Office of Statewide Health Planning and Development.
Population:
One million California live births (2007-10) after live birth and after pregnancy termination.
Methods:
Logistic regression was used to estimate odds ratios (ORs) of PTB of 20-36 weeks of gestation and its subcategories for IPIs after a live birth and after a pregnancy termination. We used conditional logistic regression (two IPIs/mother) to investigate associations within mothers.
Main Outcome Measure:
PTB relative to gestations of ≥ 37 weeks.
Results:
Analyses included 971 211 women with IPI after live birth, and 138 405 women with IPI after pregnancy termination with 30.6% and 74.6% having intervals of <18 months, respectively. IPIs of <6 months or 6-11 months after live birth showed increased odds of PTB adjusted ORs for PTB of 1.71 (95% CI 1.65-1.78) and 1.20 (95% CI 1.16-1.24), respectively compared with intervals of 18-23 months. An IPI >36 months (versus 18-23 months) was associated with increased odds for PTB. Short IPI after pregnancy termination showed a decreased OR of 0.87 (95% CI 0.81-0.94). The within-mother analysis showed the association of increased odds of PTB for short IPI, but not for long IPI.
Conclusions:
Women with IPI <1 or >3 years after a live birth were at increased odds of PTB-an important group for intervention to reduce PTB. Short IPI after pregnancy termination was associated with reduced odds for PTB and needs to be further explored.
Tweetable Abstract:
Short and long IPI after live birth, but not after pregnancy termination, showed increased odds for PTB.
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