The American College of Obstetricians and Gynecologists (ACOG) in its Practice Bulletin Number 143, March 2014, states that: “No evidence exists to date of a teratogenic effect of mifepristone.” In other words, it does not appear that mifepristone, RU-486, causes birth defects. Progesterone has been safely used in pregnancy for over 40 years. There is no record of birth defects caused by progesterone. The type of progesterone used for treatment is the same as the progesterone made in a woman’s body. It is sometimes called natural or bioidentical progesterone.