A,
B, C, D, and X.
Category A is the safest, while drugs in Category X are unsafe for women who are pregnant or could become pregnant.
There are not many Category A drugs, says Dr. Lund. "Prenatal vitamins are not even Category A, because if you overdose on them, they cause problems." But there are Category A drugs available for conditions such as nausea and vomiting, thyroid disorders, and gestational diabetes.