AbstractBackgroundFavipiravir is one of the essential antiviral drugs used for the treatment of coronavirus disease (COVID‐19) in some countries. However, there is not enough information about used, especially in pregnancy. Therefore, in this study, it was aimed to determine the developmental toxicity of favipiravir on fetal bone development and embryonic development.MethodsIn this study, 16 pregnant wistar albino rats were used. The rats were divided into four groups: Control (saline) and Group A (50 mg/kg × 5 days), Group B (50 mg/kg × 1 days + 20 mg/kg × 4 days), Group C (20 mg/kg × 5 days). Solutions were administered to the rats by oral gavage from the 10th to 14th days of pregnancy, twice a day. The skeletal system development of fetuses was examined with double skeletal staining and immunohistochemical staining methods.ResultsA total of 72 fetuses from pregnant rats, 18 in each group, were included in the study. As a result, depending on favipiravir dose increase, in experimental groups, it was determined that the statistically significant decrease on the ossification rates of anterior and posterior extremity bones, and length and weight of fetuses.ConclusionExposure to favipiravir during pregnancy impairs bone metabolism and bone formation‐resorption stages and may cause developmental delay.