Part of the first prenatal visit will include a detailed account of your personal medical history, including all the medications and supplements you currently take. While some medicines are safe to use during pregnancy, others may cause birth defects and should be stopped as soon as possible.
In the United States, the FDA gives drugs a pregnancy rating: A, B, C, D and X. Medications rated category A and B are generally considered safe during pregnancy because they haven't been shown to cause any problems when used by pregnant women. Drugs in category C have unknown outcomes for pregnant women -- studies haven't determined whether they're safe or not. Those rated D have caused harm to some fetuses, and those rated X are considered off-limits to pregnant women.
While many women try to avoid taking any medications during their pregnancies, sometimes that's not an option -- it's a decision you and your doctor will make based on whether or not the benefits outweigh the risks. Depending on the condition your medication is treating, you may be advised to stop taking it, or your doctor may prescribe a different drug that's considered safer for your growing fetus. Take a list of all your medications to your first appointment so you and your doctor can decide what's best for you.