The effect of contraceptive use at the time of pregnancy on spontaneous and induced abortion

Ortega, José Antonio [Universidad de Salamanca] Sánchez-Páez, David Antonio [UCL]

Background: Literature on pregnancy outcomes generally indicates the relevance of contraceptive use at the time of pregnancy. Users are more likely to recur to induced abortion,but also spontaneous abortion might differ according to contraceptive use. Many studies donot account properly for the competing risk between pregnancy outcomes. Methods: Based on pregnancy and contraceptive calendar data, we analyse the outcomesof 32,545 pregnancies of women aged 15-49 from 10 DHS surveys collected between 2003and 2012 that did report on pregnancy outcomes. We present binomial and multinomialregression estimates of the effects of contraceptive use on the odds of pregnancy termination. Results: Contraceptive users are more likely to end their pregnancies by an induced abortion, and less likely to suffer from spontaneous abortion, but the second effect is mainly due to the competing risk between both outcomes. Younger users experiencing contraceptive failure are more likely to abort than non-users. There are no systematic patterns regarding spontaneous abortion once we controlfor the competing risk. Discussion: The results indicate the need to control for competing pregnancy outcomes, andthat most of the differences in the probability of termination are connected to induced abortion. Induced abortion is particularly likely for younger women who experienced contraceptive failure.