Is induced abortion with misoprostol a risk factor for late abortion or preterm delivery in subsequent pregnancies?

To examine whether a first or second trimester induced abortion with misoprostol influences the risk of late abortion or preterm delivery in subsequent pregnancies.

Case-control study in a teaching hospital from January 2005 to June 2006. The cases had singleton pregnancies delivered at 16-36 weeks of gestation after spontaneous late abortions, preterm labor or preterm premature rupture of membrane, or induction of labor for preterm premature rupture of membrane before 37 weeks. The control group was composed of the two consecutive spontaneous singleton deliveries at >or=37 weeks of gestation after each new case (ratio 2/1). The principal outcome measure was late abortion or preterm delivery. The association between late abortion or preterm delivery and a previous induced abortion with misoprostol was first assessed with the Cochran-Mantel-Haenszel chi-square test. Conditional logistic regression models adapted for clustered data were then further used to quantify the effect size, measured by estimated odds ratios (ORs) with their 95% confidence intervals (95% CI).

The study included 245 cases and 490 controls. There was no significant difference in mean maternal age, number of pregnancies, parity, smoking, or history of first trimester miscarriage between cases and controls. However, a history of late abortion or previous preterm delivery was significantly more frequent among cases than controls. Forty (16.3%) cases and 56 (11.5%) controls had a history of cervical ripening with misoprostol before vacuum curettage or evacuation, or of medical abortion by misoprostol alone or with mifepristone (OR 1.51, 95% CI: 0.95-2.39; p=0.08). After adjustment for maternal age and number of pregnancies with a multivariable conditional regression model, the adjusted OR was estimated at 1.33 (95% CI: 0.81-2.17; p=0.25).

Despite the need for prudence, these results provide some reassurance that induced abortion with misoprostol during the first or second trimester of pregnancy is safe for subsequent pregnancies.