Objectives: To examine the association between prior induced abortions and prematurity and to explore potential mechanisms for a relationship, including second trimester pregnancy losses and infections.
Methods: We conducted a retrospective review of the records of all women who delivered between April 2001 and March 2006 using data from the McGill Obstetric and Neonatal Database. Exposure was categorized as having had no prior induced abortions, one prior induced abortion, or two or more prior induced abortions. Our primary outcome was gestational age at delivery, categorized as < 24 weeks, < 26 weeks, < 28 weeks, < 32 weeks and < 37 weeks. Secondary outcomes were intrapartum fever, NICU admission, and use of tocolysis.
Results: A total of 17 916 women were included in the study. Of these 2276 (13%) had undergone one prior induced abortion, and 862 (5%) had undergone two or more prior induced abortions. Women with a prior induced abortion were more likely to be smokers and to consume alcohol, and were less likely to be married. Women who reported one prior induced abortion were more likely to have premature births by 32, 28, and 26 weeks; adjusted odds ratios were 1.45 (95% CI 1.11 to 1.90), 1.71 (95% CI 1.21 to 2.42), and 2.17 (95% CI 1.41 to 3.35), respectively. This association was stronger for women with two or more previous induced abortions. Prior induced abortion was associated with an increased requirement for tocolysis in subsequent pregnancies, but there was no association between prior induced abortions and NICU admission, intrapartum fever, and preterm premature rupture of membranes.
Conclusion: Our study showed a significant increase in the risk of preterm delivery in women with a history of previous induced abortion. This association was stronger with decreasing gestational age.