Related Experiment Video
Updated: Nov 29, 2025

Modeling Ascending Vaginal Infection, Preterm Birth, and Neonatal Morbidity in Mice
Published on: October 10, 2025
Associations between interpregnancy interval and preterm birth by previous preterm birth status in four high-income
M L Marinovich1, A K Regan2, M Gissler3,4
1School of Public Health, Curtin University, Perth, WA, Australia.
Objective:
To investigate the effect of interpregnancy interval (IPI) on preterm birth (PTB) according to whether the previous birth was preterm or term.
Design:
Cohort study.
Setting:
USA (California), Australia, Finland, Norway (1980-2017).
Population:
Women who gave birth to first and second (n = 3 213 855) singleton livebirths.
Methods:
Odds ratios (ORs) for PTB according to IPIs were modelled using logistic regression with prognostic score stratification for potential confounders. Within-site ORs were pooled by random effects meta-analysis.
Outcome Measure:
PTB (gestational age <37 weeks).
Results:
Absolute risk of PTB for each IPI was 3-6% after a previous term birth and 17-22% after previous PTB. ORs for PTB differed between previous term and preterm births in all countries (P-for-interaction ≤ 0.001). For women with a previous term birth, pooled ORs were increased for IPI <6 months (OR 1.50, 95% CI 1.43-1.58); 6-11 months (OR 1.10, 95% CI 1.04-1.16); 24-59 months (OR 1.16, 95% CI 1.13-1.18); and ≥ 60 months (OR 1.72, 95%CI 1.60-1.86), compared with 18-23 months. For previous PTB, ORs were increased for <6 months (OR 1.30, 95% CI 1.18-1.42) and ≥60 months (OR 1.29, 95% CI 1.17-1.42), but were less than ORs among women with a previous term birth (P < 0.05).
Conclusions:
Associations between IPI and PTB are modified by whether or not the previous pregnancy was preterm. ORs for short and long IPIs were higher among women with a previous term birth than a previous PTB, which for short IPI is consistent with the maternal depletion hypothesis. Given the high risk of recurrence and assuming a causal association between IPI and PTB, IPI remains a potentially modifiable risk factor for women with previous PTB.
Tweetable Abstract:
Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB.
More Related Videos
14:43A Novel Method for Involving Women of Color at High Risk for Preterm Birth in Research Priority Setting
Published on: January 12, 2018
07:36Modeling Encephalopathy of Prematurity Using Prenatal Hypoxia-ischemia with Intra-amniotic Lipopolysaccharide in Rats
Published on: November 20, 2015
Related Concept Videos
Regression Toward the Mean
Confounding in Epidemiological Studies
Bias in Epidemiological Studies
Prevalence and Incidence
Prevalence indicates the proportion of individuals in a population who have a specific disease or health...
Prediction Intervals
However, the point estimate is most likely not the exact value of the population parameter, but close to it. After calculating point estimates, we construct interval estimates, called confidence intervals or prediction intervals. This prediction interval comprises a range of values unlike the point estimate and is a better predictor of the observed sample value, y.