Recurrence risk of preterm birth in successive pregnancies based on its subtypes.

Abstract

Objective: Preterm birth (PTB) remains one of the biggest public health challenges with both obstetric and perinatal implications. While a prior PTB is a known risk factor for recurrence, the understanding of the influence of factors such as race/ethnicity, gestational age, PTB subtypes, and interpregnancy intervals (IPI) remains limited. This study aimed to assess whether these factors modify PTB recurrence risk.

Methods: We conducted a retrospective cohort study of singleton pregnancies in Kaiser Permanente Southern California (2009-2022) using electronic health record data from 82,610 women with two pregnancies and 14,925 women with three. PTB subtypes, spontaneous (sPTB) and indicated (iPTB), were identified through natural language processing. Logistic regression was used to estimate adjusted odds ratios (aOR) and 95% confidence intervals (CI).

Results: A first PTB was associated with a 6-fold increased risk of PTB in the second pregnancy compared to an uncomplicated pregnancy (23.29% vs. 4.98%, respectively; aOR, 5.60, 95% CI: 5.23-5.99). Those with a history of sPTB (aOR: 5.32, 95% CI: 4.87, 5.81) and iPTB (aOR: 8.26, 95% CI: 7.18, 9.50) had increased risk for the same respective subtype at their second pregnancy. PTB recurrence risk persisted across race/ethnicity categories. In women with PTB in both prior pregnancies, the risk for PTB in a third pregnancy was significantly higher (aOR 14.59, 95% CI 11.28-18.88). The recurrence of PTB between 1st and 2nd pregnancy was substantially higher for those who delivered at 20-33 weeks of gestation, regardless of PTB subtype. Non-Hispanic Black and Asian/Pacific Islander women had higher recurrence risk compared to non-Hispanic Whites.

Conclusion: These findings highlight disparities in PTB recurrence by race/ethnicity and PTB subtype among a large integrated healthcare system in Southern California, underscoring the need for targeted interventions, particularly for sPTB.