The impact of interpregnancy interval and previous preterm birth on the subsequent risk of preterm birth

OBJECTIVE: To examine the impact of the interpregnancy interval and a previous preterm birth on the subsequent risk of a preterm birth. METHODS: A retrospective analysis was conducted on a group of 4072 women who had at least two consecutive births, excluding multiple gestation, fetal anomalies, cervical incompetence, and stillbirth. Multivariate logistic regression was used to investigate the association between interpregnancy interval, preterm birth of the first child in the pair (index pregnancy), and the risk of a preterm birth of the second child in the pair (outcome pregnancy). RESULTS: Women with interpregnancy intervals of less than 12 months (odds ratio [OR] 1.3; 95% confidence interval [CI] 1.0-1.7) were at increased risks of preterm birth with the outcome pregnancy. Furthermore, there was an increased risk for a subsequent preterm birth in women who had a preterm birth in the index pregnancy (OR 4.2; 95% CI 3.0-6.0). The risk decreased as the interpregnancy interval increased, with a relatively low risk at 18 to 48 months; subsequently, it increased sharply. In contrast, women who had delivered their previous infants at term carried an increased risk of preterm birth with the outcome pregnancy only if the interval was less than 6 months. CONCLUSION: A difference was found in the impact of the interpregnancy interval on the subsequent risk of preterm birth between women with a prior preterm birth and those who previously delivered an infant at term.