Variation in risk factors and timing of birth for different types of preterm birth: A historical cohort study.

Abstract

Introduction: The aim of this study was to investigate the risk factors and timing of birth for different types of preterm birth, including iatrogenic preterm birth, spontaneous preterm birth, and preterm prelabor rupture of membranes across health services in New South Wales, Australia.

Material and methods: We conducted a historical cohort study between 2018 and 2023 using routinely collected electronic data across four local health districts in New South Wales. Maternal characteristics and outcomes were compared using summary statistics. Differences in the incidence of each preterm birth type were compared using multivariate logistic regression models. Cox regression was performed to assess the time-to-event for each preterm birth type and account for confounders.

Results: A total of 113 244 singleton pregnancies were included, of which 7940 (7.0%) were born preterm. Of these, 3909 (49.2%) were iatrogenic preterm births, 2931 (36.9%) were spontaneous preterm births, and 1100 (13.9%) had preterm prelabor rupture of membranes. Iatrogenic late preterm (32-36 weeks' gestation) births accounted for 38.8% of all preterm births. All three categories of preterm birth were strongly associated with a history of previous preterm birth and model of antenatal care. Among higher capacity (level 4-6) maternity hospitals, there was significant variation in the gestational age of birth for those with preterm prelabor rupture of membranes and iatrogenic preterm birth affected by hypertensive disorders of pregnancy or pre-eclampsia.

Conclusions: There was a high rate of iatrogenic preterm birth, especially in the late preterm period. There is variation in the timing of birth in higher capacity maternity hospitals, suggesting different management approaches and/or unmeasured confounding factors.