Medically there aren't any reasons since the alternative is usually the more dangerous option. There are however reasons why you can't have a medical abortion but should have a surgical instead and those are (Source: Planned Parenthood):
- are more than 63 days - nine weeks - pregnant
- are not willing to have an aspiration abortion in the unlikely case that the medicines do not end your pregnancy
- cannot come to follow-up appointments
- do not have access to a telephone, transportation, and backup medical care
- have a known or suspected molar pregnancy - one in which the placenta develops abnormally
- have severe adrenal gland, heart, kidney, or liver problems
- take any medicine that should not be combined with the medications used in medication abortion - mifepristone or misoprostol
- take anti-clotting medication or have a blood-clotting disorder
- currently have an IUD. You will need to have it removed before having a medication abortion.
You can not have an abortion if you are passed the legal limit, in the US week 20 or 24 depending on which state, but always for health reasons. Passed week 24 it's premature labor though.
