The aim of our study was to study the possible correlation between use of antibacterial drugs in pregnancy and occurrence of congenital malformations. Among 6099 investigated pregnant women, 392 (6.43%) used antibacterial drugs. The most frequently used antibacterials belonged to category B (75.77%), while 14.54% antibiotics belonged to category D and 1.02% to category X. The most often used antibiotics were cephalexin (22.19%), amoxicillin (20.66%) and ampicillin (14.29%). In 14 embryos exposed to effects of beta-lactams in utero, malformations were detected. The results of this study show possible teratogenic potential even with those antibacterials which are considered safe, but as those are usually minor malformations, they often pass undetected. Because of that and because of frequent use of antibacterials during pregnancy, detailed examinations concerning their safety should be made.