Women with threatened preterm labour followed by term delivery have an increased risk of spontaneous preterm birth in subsequent pregnancies: a population-based cohort study

Abstract

Objectives To evaluate the association of a history of threatened preterm labour (TPL) followed by term delivery with the risk of spontaneous preterm delivery (PTD) in subsequent pregnancy. Design Population-based cohort study. Setting Data of the National Health Insurance Claims Database and a national health-screening programme for infants and children in South Korea. Population Women who had their first singleton delivery in 2010 and a subsequent second singleton delivery between 2011 and 2015. Methods Multivariable analysis adjusting for maternal age and interval between first and second deliveries was used to assess the risk of PTD based on PTD, TPL followed by term delivery, and term delivery in the first pregnancy. Main outcome measures The risk of PTD during the second pregnancy. Results This study included 115 629 women with two consecutive deliveries during the study period. Spontaneous PTD rates in the second pregnancy were 7.71, 2.22 and 1.02% in women with PTD, TPL followed by term delivery, and term delivery in the first pregnancy, respectively. Threatened preterm labour followed by term delivery in the first pregnancy was associated with increased risk of PTD in the subsequent pregnancy after adjustment for potential confounding factors (adjusted odds ratio 2.21; 95% CI 1.76-2.78). Conclusion Although women with a history of TPL followed by term delivery had a lower risk of PTD during a subsequent pregnancy compared with those with history of previous PTD, they still had a significantly increased risk of PTD compared with those who delivered at term without TPL.