Recurrent preterm birth across three consecutive pregnancies: A retrospective cohort study in a tertiary care center

Preterm birth (PTB) remains a leading cause of neonatal morbidity and mortality globally. A prior PTB is a recognized predictor of recurrence; nonetheless, most existing studies have limited their focus to the first two pregnancies. We aimed to evaluate the risk of recurrent PTB across three consecutive singleton pregnancies. This retrospective cohort study analyzed data from 97,854 women with singleton pregnancies. Participants were stratified based on the gestational age at their first delivery, and PTB outcomes in subsequent pregnancies were assessed. Additionally, a sub-analysis of 11,760 women with three consecutive deliveries was conducted to assess the cumulative risk of recurrent PTB. The adjusted relative risk (aRR) for PTB was estimated using multivariable models. Among the study population, 12.3% (n=12,036) experienced PTB in their first pregnancy, of which 10.1% were spontaneous and 2.2% were medically indicated. The risk of PTB in the second pregnancy demonstrated an inverse relationship with gestational age at the first delivery: 8.6% for term, 19% for 34–36⁶ weeks, 25.9% for 32–33⁶ weeks, and 29.3% for deliveries under 32 weeks. The aRR for PTBs in the second pregnancy were 3.72 (34–36⁶ weeks), 5.65 (32–33⁶ weeks) and 6.21 (<32 weeks) compared with term births. The risk of PTB in the third pregnancy was lowest among women with two prior term births (4.8%) and increased progressively with each prior PTB: 15.6% (aRR=3.38) with preterm/term, 19.1% (aRR=5.34) with term/preterm, and 29.7% (aRR=9.87) with two prior PTBs. The likelihood of recurrent PTB rises with the number of previous preterm deliveries, being highest among women with two consecutive PTBs. A term delivery, especially as the most recent pregnancy, has a protective effect. By extending risk assessment to third pregnancies, this study provides novel insights that may guide targeted prevention strategies and improve counseling for women at elevated risk.