Risk of spontaneous abortion following induced abortion is only increased with short interpregnancy interval.

We set out to study the risk of spontaneous abortion following a first trimester induced abortion as a function of the interpregnancy interval between two pregnancies. The cohort study is based on the following databases: Danish national registries: the Medical Birth Registry (MBR), the Hospital Discharge Registry (HDR), and the induced Abortion Registry (IAR). All primigravid women in the time period from 1980 to 1982 were identified in the MBR, the HDR and the IAR. A total of 15 727 women who terminated the pregnancy with a first trimester induced abortion were selected as the induced abortion cohort, and 46 026 women who did not terminate the pregnancy with an induced abortion constituted the control cohort. By register linkage all subsequent pregnancies which were not terminated by induced abortion were identified from 1980 to 1994. Only women who had a non-terminated pregnancy following the index pregnancy were selected. Women whose first pregnancy was terminated following a first trimester induced abortion had a risk of spontaneous abortion of 11.0% vs. 9.4% in the control cohort. This relative difference of 1.17 was not statistically significant in logistic regression analyses. An increased risk was only found for women who had an interpregnancy interval of less than 3 months (OR=4.06, 95% C.I.=1.98-8.31). The abortion method, vacuum aspiration with dilatation or evacuation with dilatation did not modify this elevated risk. Overall the study did not show an increased risk of spontaneous abortion following one or more induced abortions, except for women with a short interpregnancy interval between an induced abortion and a subsequent pregnancy. We recommend women who have a first trimester induced abortion be advised to wait at least 3-6 months before trying to become pregnant again.