Birth defects are a major contributor to the rate of deaths among newborns (infant mortality). In the 1940s, rubella infection during pregnancy was found to have devastating effects on the fetus, from fetal death to hearing impairment, cataracts, and heart defects. Twenty years later, the perception of the placenta as a barrier against drugs changed. Women taking thalidomide during early pregnancy gave birth to children with severe limb deformities. Thus, the placenta did not protect the fetus against environmental factors (e.g., teratogens), such as infectious agents and chemical agents (drugs). Furthermore, birth defects with a genetic origin could be inherited from parents via the fetus. In the early 1990s, folic acid supplementation was found to reduce the occurrence of neural tube defects and other kinds ...