A majority of pregnant women take at least one medication during pregnancy, although the safety of such drugs during pregnancy is not always known. We reviewed the safety during pregnancy of 172 drugs approved by the US Food and Drug Administration (FDA) from 2000 to 2010 using the TERIS risk rating system. We also reviewed safety information for 468 drugs approved by the FDA from 1980 to 2000 to determine if revisions in risk categories had been made in the last 10 years. The teratogenic risk in human pregnancy was “undetermined” for 168 (97.7%) of drug treatments approved between 2000 and 2010. Furthermore, the amount of data available regarding safety in pregnancy was rated as “none” for 126 (73.3%) of these drugs. For those drugs approved between 1980 and 2000, only 23 (5%) changed a full risk category or more in the past 10 years. Sources of data that led to a revised risk were derived from exposure cohort studies performed through record linkage studies, teratogen information services, large population-based case-control studies, and pregnancy registries. The mean time for a treatment initially classified as having an “undetermined” risk to be assigned a more precise risk was 27 years (95% confidence interval 26–28 years). The lack of information needed to assess the safety of drug treatments during human pregnancy remains a serious public health problem. A more active approach to post-marketing surveillance for teratogenic effects is necessary. © 2011 Wiley-Liss, Inc.