Purpose: To evaluate the role of infection as a cause of pregnancy loss. Methods: Studies concerning the risk factor of certain microorganisms for first trimester miscarriage and premature rupture of membranes are reviewed. The microorganisms especially considered were ureaplasma/mycoplasma, the potpourri of organisms causing bacterial vaginosis and chlamydia trachomatis. Results: The consensus is that all these microorganisms can on occasion lead to first trimester spontaneous abortion and second trimester loss especially related to premature rupture of membranes. Conclusions: Reactivation during pregnancy is possible so the best strategies involve giving a course of appropriate antibiotics prior to pregnancy but giving antibiotics at least intermittently during the first trimester. Similar antibiotic therapy could be considered for unexplained recurrent miscarriage where negative cultures exist.