When your doctor learns that you’re pregnant, one of the first things they’ll do is give you a blood test to find out your Rh factor. The Rh factor is a protein in the blood. If you have it, you’re Rh-positive. If you don’t, you’re Rh-negative. Most people are Rh-positive.
Parents pass along their Rh-factor status to their babies. When one parent is Rh-positive and one is Rh-negative, there’s a roughly 50-50 chance that the mom and baby’s Rh-factor status will match. Your doctor needs to know your status because your baby can develop a serious health problem if they’re Rh-positive and you’re Rh-negative. This is called Rh incompatibility.
What Is Rh Sensitization?
When you’re Rh-negative, your body treats Rh-positive blood that you come in contact with as a foreign substance and builds antibodies to protect itself. This is known as Rh sensitization. Your doctor will give you a blood test at the beginning of your pregnancy to determine if you have any antibodies in your blood.
Rh sensitization is unlikely to harm the first Rh-positive baby that you carry because you’ll rarely come into contact with your baby’s blood until labor and delivery, meaning the antibodies won’t be created until after the birth.
But once you are Rh sensitized, the Rh antibodies stay in your system. If you get pregnant with a second Rh-positive baby, your Rh antibodies will attack this baby’s blood while they’re growing inside of you. This can cause Rh disease in your baby.
Rh disease causes hemolytic anemia, which destroys red blood cells faster than the body can create them. It can cause serious illness or even death for your baby.
Exposure to Rh-Positive Blood
Even though you and your baby don’t share blood, some of your baby’s blood can mix with yours for various reasons. Most of the time it happens during labor and delivery, but it can also happen:
- During amniocentesis, which is a test that uses a needle to extract cells from the fluid that surrounds your baby inside the womb.
- During chorionic villus sampling (CVS), which is a test that uses a long needle to extract cells from the placenta (tissue within your womb that you use to nourish your baby).
- If you have vaginal bleeding when you’re pregnant.
- If you sustain an injury to your belly while you’re pregnant.
- If your baby is breech (feet-first) and your doctor tries to turn them around by pressing on your belly.
- If you have a miscarriage, an ectopic pregnancy (a life-threatening problem that happens when a baby starts to grow outside the womb), or an abortion.
Do I Need Rh Treatment?
If you’re Rh-negative but not yet Rh sensitized, your doctor can prevent your body from making Rh antibodies with an injection of a medication, called Rho(D) immune globulin (RhoGAM). You’ll get one when you’re 28 weeks pregnant and a second within 72 hours after your baby is born.
If you have to get an amniocentesis or CVS, your doctor may give you an injection afterward, just to be safe. They may also give you one after you have a miscarriage, abortion, or ectopic pregnancy, since these could all expose you to Rh-positive blood.
If your blood test shows that you’re Rh-negative, and already have Rh antibodies, your doctor may want to do an amniocentesis to find out if your baby is Rh-positive. At this point, the Rho(D) immune globulin medicine can’t do anything to help. Your doctor will need to keep a close eye on your baby’s health, watching for signs of Rh disease.
How are Babies Treated for Rh Disease?
Whether or not your baby needs treatment for Rh disease depends on whether it’s a mild or severe case. Some babies have only mild anemia and don’t need a doctor’s help, or they may only need medication.
Other babies with Rh disease can have severe anemia, as well as jaundice (the skin turns yellow due to a liver problem), brain damage, or serious heart problems. Being exposed to special lights (phototherapy) can improve the jaundice. A blood transfusion can improve the anemia.
Sometimes, a baby needs to have a blood transfusion while you’re still pregnant (this can be done through the umbilical cord). Other times, a baby doesn’t need a blood transfusion until after birth. In serious cases, you may have to deliver your baby early (at 37 weeks) so they can have a blood transfusion.