 Abnormal vaginal flora is a risk factor for preterm labor. Therefore, in high risk pregnancies for preterm labor the diagnosis and treatment of abnormal flora is indicated. Clindamycin and metronidazole given orally are both acceptable treatments in these cases. The purpose of this study is to compare the effectiveness of Clindamycin Vs metronidazole for the treatment of abnormal vaginal flora in high risk pregnancies. For this purpose, pregnant women who are considered high risk for preterm labor and were diagnosed with abnormal vaginal flora will be randomly treated either with clindamycin or metronidazole. Eradication of the abnormal flora and adverse effects will be monitored and compared 