What is Rhesus Incompatibility and What Does It Mean for Using the Abortion Pill?

When you're making medical decisions, such as whether or not to take abortion pills, it's important to keep in mind your medical history, as well as any current realities about your health. If you've had an allergic reaction to mifepristone or misoprostol in the past, an ectopic pregnancy, adrenal or liver failure, or inherited porphyria, you should not use abortion pills. Other situations, such as being Rhesus (Rh) negative, do not impact your ability to self manage your abortion.

Rhesus factor is an inherited protein that's found on the surface of red blood cells. If you have this protein, which can be assessed via a blood test, that means you're Rh positive, which is what most people are. Without the protein, you're Rh negative. The positive or negative is indicated with a "+" or "-" after your blood type (for example, "O+"  or "B-").

When a pregnant person is Rh negative, and their fetus is Rh positive, the pregnant person's body may generate an antibody that can damage the fetus's red blood cells. If the pregnant person wants to stay pregnant, she may receive an injection known as a RhoGAM (Rh-immunoglobulin injection) shot in order to stop antibodies from forming. This injection may be given during week 28 of pregnancy and then again within 72 hours after delivery to ensure that future pregnancies are safe.

So what does this mean if you're Rh negative and planning on using abortion pills? If you're up to 63 days (9 weeks) pregnant, there's no reason to get an injection of any sort before or after taking the pills, since there's no evidence that any problem related to blood groups can occur this early in pregnancy. After 9 weeks, however, the pregnant person should get a RhoGAM shot the same day they take the mifepristone or misoprostol or maximum up to 72 hours after the abortion to avoid Rh incompatibility in the future.  This is why it's super important to know whether you're Rh positive or negative, and why it's also important to abortion pills as soon as you can once you confirm your pregnancy. The mifepristone/misoprostol combination is 95-98% effective to 11 weeks, and you can take misoprostol on its own up until 12 weeks of pregnancy, and in this case, it's 80-85% effective.

Don't let abortion stigma get in the way of your access to abortion care. When abortion is safe, it does not endanger your ability to get pregnant in the future. This is true of both abortion pills and surgical abortion. For information on abortion pills, how to get them, how they work, what to expect, and more, visit our FAQs.