Recurrent Risk of Preterm Birth in the Third Pregnancy in Korea.

Background: Although preterm delivery is the most common cause of infant morbidity and mortality, an obvious cause cannot be found in most cases. Preterm delivery is known to be the most important risk factor for preterm birth in a subsequent pregnancy. We aimed to evaluate the recurrence rate of premature births for subsequent pregnancies in women with a history of a preterm birth.

Methods: Study data were collected from the Korea National Health Insurance (KNHI) claims database and data from a national health-screening program for infants and children. We enrolled women who had their first delivery between January 1, 2007 and December 31, 2007 and a subsequent delivery before 2014.

Results: Preterm delivery had a significant higher risk of preterm birth in a subsequent singleton pregnancy. The risk of preterm birth at second pregnancy was 2.2% in women whose first delivery at ≥ 37 weeks and 18.6% in women whose first delivery at < 37 weeks (relative risks [RR], 8.64; 95% confidence interval [CI], 7.94-9.40). In the analysis of the third pregnancy, we compared women with an initial term birth followed by preterm birth and women with an initial preterm birth followed by a subsequent term birth. A history of a just preceding preterm birth at < 37 weeks was the most relevant factor for recurrence of preterm delivery in a subsequent pregnancy (26.6%, RR, 4.01; 95% CI, 2.45-6.58).

Conclusion: We found that the prognosis of a third pregnancy was more closely related to the outcome of the second pregnancy to that of the first pregnancy.