Differences in efficacy, differences in providers: results from a hazard analysis of medical abortion.

Sample sizes of even the largest medical abortion trials are generally not adequate to provide an understanding of how well the regimen works for subgroups of women, particularly when controlling for factors known to influence efficacy, such as gestational age. By pooling data from four previously published studies of medical abortion and using hazard analyses, we can undertake such an investigation. We find that women with lower gestational ages, women younger than 23 years of age, women with more than 12 years of education and women with no previous induced abortion experience were more likely to experience a successful medical abortion. After taking into account demographic factors, we find that significant differences in efficacy persist across study sites, indicating that differences in providers' tendency to intervene by performing vacuum aspiration vary across medical abortion providers.