Just over half a century ago, not much was known about placental drug transfer and metabolism and in utero exposure risks to the fetus. This allowed for the liberal use of pharmaceuticals antenatally that eventually cumulated in the thalidomide crisis of the 1950s. Frances Kelsey, PhD, a physician-pharmacist and drug reviewer for the US Food and Drug Administration (FDA), astutely withheld the approval of thalidomide in the US due to limited safety data, preventing thousands of potential fetal malformations. A unanimous FDA amendment in 1962 called for the rigorous protection of pregnant patients and their fetuses from the harmful effects of pharmaceuticals, leading to the firm exclusion of all people of child-bearing potential from early-phase clinical trials. In the ensuing decades, though created with good intentions, these safeguards have severely limited safety data for the therapeutic use of many essential medications for pregnant patients.