ObjectiveTo study the human teratogenic risk of doxycycline treatment during pregnancy.MethodsPaired analysis of cases with congenital abnormalities and matched healthy controls was performed in the large population-based data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980–1992.ResultsOf 32,804 pregnant women who had infants with no defects in the study period (control group), 63 (0.19%) were treated with doxycycline. Of 18,515 pregnant women who had offspring with congenital abnormalities, 56 (0.30%) were treated with doxycycline, a rate that is higher than that of the control group (P= .01). However, the case-control pair analysis did not show a significantly higher rate of doxycycline treatment in the second and third months of gestation in any group of congenital abnormalities.ConclusionsTreatment with doxycycline during pregnancy presents very little if any teratogenic risk to the fetus. Thus, if doxycycline treatment is necessary during pregnancy, there would appear to be no contraindication.