On the role of 'habitual aborters' in the analysis of spontaneous abortion.

Analyses of spontaneous abortion rates often include special provisions to account for the presumed distorting effects that arise because of the presence of habitual aborters. In this paper, I establish a framework for investigating the effects of the presence in study groups of such women. I then examine the strengths and weaknesses of some of the analysis strategies in current use, both in situations where the study group is homogeneous and where there are high-risk women present. I show that the concept of habitual aborter is not useful and can be misleading, and I suggest that one take a broader view of heterogeneity.