In scanning recent studies done on miscarriages, I came across the abstract for a study published in May in European Journal of Obstetrics & Gynecology and Reproductive Biology called "Recurrent miscarriages: Are three miscarriages one too many?"
In the study, researchers analyzed medical records documenting 151,021 pregnancies in Scotland from 1950-2000. After the researchers adjusted for maternal age and smoking, study of the records indicated that the odds of further miscarriage were increased in women with one previous miscarriage compared to women with no previous miscarriages, and the odds were further increased in women with two previous miscarriages compared to women with one, but chances of miscarriage were not increased in women with three previous miscarriages compared to women with two.
Though I can imagine that there might be some limitations to such a study, the results were interesting, as it would seem to support the idea that testing for causes of recurrent miscarriages might make sense in women who have had two miscarriages rather than telling such women that they will have to miscarry again before they can receive tests. And although many practitioners still wait for the third miscarriage before initiating testing, it's interesting that the American College of Obstetricians and Gynecologists defines repeated miscarriage as being "consecutive loss of two or more pregnancies before 20 weeks of pregnancy."