Abstract. – Background and Objectives: During pregnancy, a number of changes occur in women`s body, and some medications are safe and some are not. The aim of our study was to establish the possible correlation between use of β-lactam antibiotics in pregnancy and occur- rence of congenital malformations. Material and Methods: The study included 893 pregnant women from Zagreb and 6099 preg- nant women from Novi Sad. 527 pregnant women used β-lactams. First part of the study (one month study) was performed at four maternity hospitals in Zagreb, Croatia. Second part were collected as a part of the study analysing the teratogenicity of drugs used in pregnancy, a longitudinal study per- formed in Novi Sad district. Results: Pregnant women most frequently used antibacterial agents in the first trimester of pregnancy. They used 15 different antibacterial medications, most often β-lactams. In Zagreb arm, out of the total number of pregnant women that used medications during pregnancy (859), 231 (26.9%) used β-lactam antibiotics. Malforma- tions were detected in 8 (3.5%) cases. The preva- lence of malformations in newborns whose mothers did not take β -lactam antibiotics in pregnancy (662) was 2.7% (18 newborns with malformations). In Novi Sad arm, out of the total number of pregnant women that used medica- tions during pregnancy (2013), 296 (14.7%) used β-lactam antibiotics. Malformations were detect- ed in 14 (4.7%) cases. The prevalence of malfor- mations in newborns whose mothers did not take β-lactam antibiotics in pregnancy (5803) was 1.7% (99 newborns with malformations). Discussion: The results show possible terato- genic potential even with those antibacterials which are considered safe (amoxicillin) but as those are usually minor malformations they of- ten pass undetected. International pharmacoepi- demiological studies of drug use in pregnancy could substantially contribute to the improve- ment of pharmacotherapy, and could be of great help in assessing the fetal risks. European Review for Medical and Pharmacological Sciences Corresponding Author: Marcel Leppée, MD; e-mail: marcel.leppee@stampar.hr 103 Key Words: β-lactam antibiotics, Pregnancy, Congenital malfor- mations, Zagreb, Novi Sad. Introduction During pregnancy, a number of changes occur in women’s body, and some medications are safe and some are not. Some require a higher than usu- al dose, and some doses change with the advanc- ing pregnancy. Prescribing drugs during pregnan- cy poses a challenge to the physician to balance optimal treatment of the maternal symptoms and disease against possible harm to the foetus 1,2 . Pharmacoepidemiological studies dealing with prescription of drugs in pregnancy are numer- ous 1-2,4,5 . Epidemiological studies of pregnancy outcome after specific drug exposures are often superficially reassuring, but most are severely limited in their power to detect adverse outcomes 6 . Results showed, that only exception- ally drugs that are used in pregnancy have been proven teratogenic. However, little is known about subtle effects of drugs on fetal develop- ment, particularly when dealing with old drugs 7-8 . Controlled studies of drug use during pregnancy cannot be performed for ethical reasons. There- fore, data can only be obtained from animal ex- periments, general databases, professional litera- ture, and individual reports on sporadic use of drugs in pregnancy 9 . According to the Food and Drug Administra- tion (FDA) all drugs can be classified in five risk groups. Risk factors (A, B, C, D and X) have been assigned to all drugs on the level of risk the 2012; 16: 103-110 β-lactam antibiotics during pregnancy: a cross-sectional comparative study Zagreb-Novi Sad M. ERIĆ 1 , M. LEPPÉE 2 , A. SABO 3 , J. CULIG 2,4 1 Department of Anatomy, School of Medicine, University of Novi Sad, Novi Sad (Serbia) 2 Department of Pharmacoepidemiology, Andrija Stampar Institute of Public Health, Zagreb (Croatia) 3 Department of Pharmacology, Toxicology and Clinical Pharmacology, School of Medicine, University of Novi Sad, Novi Sad (Serbia) 4 Department of Pharmacology, School of Medicine, Josip Juraj Strossmayer University Osijek, Osijek (Croatia)