135 women being seen at the Hospital de Maternidad Rafael Calvo, in their first, second or third trimester of pregnancy, werestudied with the intention of drawing up an infection index for Chlamydia trachomatis, Gardnerella vaginalis and other sexually transmitted diseases. Infectious microorganisms in vaginal discharge, endocervical secretion and serum from 83% of the patients were identified by means of combined laboratoty studies which included direct smears, bacteriological cultures and immunoessay techniques. 15.5% of the pregnant women had a genital infection identified as being due to C. trachomatis; 9.6%, G. vaginalk; 8.5%, Trichomonas vaginalis; 40% Candida sp.; 8.8%, Streptococcus group B; and 0.7%, Neisseriae gonorrhoeae, respectively. No patient proved to be actively infected by cytomegalovirus. As antecedents, the most frequently encountered associated pathologies were found to be cervicitis and abortion. Early membrane rupture was also presented in come patients. The significant proportion of pregnant women presenting bacteria1 infections which can lead to complications in pregnancy, merits close study when diagnosed during routine prenatal check-up at the Hospital de Maternidad Rafael Calvo.