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Rh Factor: How Does It Affect Your Pregnancy?

If you’ve just found out you’re pregnant, one of the first – and most important – tests you’ll take is a blood-type test. This simple blood test not only tells you your blood type (A, AB, B or O), it also identifies if the Rhesus protein, or Rh factor, is positive or negative.

If this is your first pregnancy, this test likely wasn’t on your radar, but knowing whether you are Rh-positive or Rh-negative is an important part of having a happy, healthy pregnancy and baby.

What’s an Rh factor and why is it important?

Rh factor is a type of specific protein found on the surface of our red blood cells that we inherit from either our mother or father. Not everyone carries this protein, but most do. If you do, you’re Rh-positive. If you don’t, you’re Rh-negative. Knowing whether you’re positive or negative doesn’t matter much for your daily activities, but it does when you’re pregnant. And here’s why.

“The concerning part is when the baby’s father is Rh-positive and the mother is Rh-negative,” said Pooja Shah, MD, an OBGYN with Banner Health Center in Chandler, AZ. “This means there’s a potential for the baby to inherit an Rh factor that is incompatible with the mother’s blood, which can cause issues down the line.”

Rh incompatibility is when a mom is Rh-negative and her baby is Rh-positive. “If the baby’s Rh-positive blood cells interact with mom’s blood cells, mom’s immune system may view the baby’s blood as a foreign invader and will mount an attack,” Dr. Shah said. “Mom’s body develops antibodies in case these types of cells return, which can happen in future pregnancies.”

When is a baby at risk?

Rh incompatibility typically isn’t a problem if it’s your first pregnancy, as these babies are born before enough antibodies develop. Most issues occur in future pregnancies with another Rh-positive baby.

During a subsequent pregnancy, your antibodies could potentially cross the placenta into your baby’s circulation and attack their blood cells. Since red blood cells carry oxygen, this can mean trouble for your baby, causing their red blood cells to swell and rupture. This is known as hemolytic or Rh disease. It can cause serious problems for your baby, including anemia, jaundice, brain damage, and in extreme cases, it can cause death.

How can Rh factor problems be prevented?

“Today, most cases of Rh disease can be prevented thanks to proper prenatal care and a medicine called Rh immunoglobulin or RhoGAM,” Dr. Shah said.

This medicine can stop your antibodies from reacting to your baby’s Rh-positive cells. Typically, you’ll receive RhoGAM during the middle of your pregnancy, around 28 weeks. You may get it earlier if you have any procedures involving the uterus, vaginal bleeding or trauma. If your baby is truly Rh-positive, a second dose will be given within 72 hours of giving birth. It is important to remember to receive RhoGAM in situations of miscarriage or ectopic pregnancy as well, in order to prevent Rh incompatibility during future pregnancies.

What happens once a baby gets Rh disease?

Babies born with mild Rh incompatibility may not require any treatment or may be treated with phototherapy using bilirubin lights. If your baby develops severe Rh disease and severe anemia, they may require blood transfusions (during pregnancy or after birth) to replace red blood cells that the Rh antibodies destroyed. They may even need early delivery to prevent worsening of the disease.

What else should I know?

“The number one thing all pregnant women should do is to receive prenatal care,” Dr. Shah said. “Rh incompatibility is preventable with early detection and treatment.”

Rh factor incompatibilities during pregnancy aren’t common, but they’re easy to find and treat. Ensure you, your baby, and any future children are protected.

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