To re-analyse the association between spontaneous and induced abortion and the risk of pelvic endometriosis, a total of 817 women with primary or secondary infertility or pelvic pain requiring laparoscopy were studied. Using women who had reported no spontaneous abortions as comparison group, the estimated odd ratios of endometriosis was 0.3 [95% IC 0.2-0.7] in those who reported at least one miscarriage. Likewise, using as comparison group women reporting no induced abortions abortion, the estimated odd ratios of endometriosis was 0.3 [95% IC 0.2-0.7] in women who had undergone one or more induced abortions. The observation of a reduced risk of endometriosis in women reporting a history of induced abortion can probably be explained by the higher fertility of women reporting induced abortions. This suggests that infertility, more than pregnancy itself, may be associated with a risk of the disease. In addition, we found no relationship between a history of miscarriage and the risk of endometriosis, suggesting that endometriosisis not associated with spontaneous abortion.
