The adult human body is home to trillions of red blood cells, also known as RBCs or erythrocytes. These blood cells carry oxygen, iron, and many other nutrients to the appropriate places in the body.

When a woman is pregnant, it’s possible that her baby’s blood type will be incompatible with her own. This can cause a condition known as erythroblastosis fetalis, where the mother’s white blood cells (WBCs) attack the baby’s RBCs as they would any foreign invaders.

This condition is highly preventable and the typical, severe form is now very rare in developed countries. Catching it early can ensure a successful pregnancy for mother and child. If left untreated, however, it can be life-threatening for the baby.

Erythroblastosis fetalis is now known as hemolytic disease of the newborn.

Babies who experience erythroblastosis fetalis symptoms may appear swollen, pale, or jaundiced after birth.

A doctor may find that the baby has a larger-than-normal liver or spleen. Blood tests can also reveal that the baby has anemia or a low RBC count.

Babies can also experience a condition known as hydrops fetalis, where fluid starts to accumulate in spaces where fluid is normally not present. This includes spaces in the:

This symptom can be harmful because the extra fluid places pressure on the heart and affects its ability to pump.

There are two main causes of erythroblastosis fetalis: Rh incompatibility and ABO incompatibility.

Both causes are associated with blood type. There are four blood types:

  • A
  • B
  • AB
  • O

In addition, blood can be either Rh positive or Rh negative.

For example, if you’re type A and Rh positive, you have A antigens and Rh factor antigens on the surface of your RBCs. Antigens are substances that trigger an immune response in your body.

If you have AB negative blood, then you have both A and B antigens without the Rh factor antigen.

Rh incompatibility

Rh incompatibility occurs when a Rh-negative mother is impregnated by a Rh-positive father. The result can be a Rh-positive baby.

In such a case, your baby’s Rh antigens will be perceived as foreign invaders, the way viruses or bacteria are perceived. Your blood cells attack the baby’s as a protective mechanism that can end up harming the child.

If you’re pregnant with your first baby, Rh incompatibility isn’t as much of a concern.

However, when the Rh-positive child is born, your body will create antibodies against the Rh factor. These antibodies will attack the blood cells if you ever become pregnant with another Rh-positive baby.

ABO incompatibility

Another type of blood type mismatch that can cause maternal antibodies against her baby’s blood cells is ABO incompatibility. This occurs when the mother’s blood type of A, B, or O isn’t compatible with the baby’s.

This condition is almost always less harmful or threatening to the baby than Rh incompatibility. However, babies can carry rare antigens that can put them at risk for erythroblastosis fetalis.

These antigens include:

  • Kell
  • Duffy
  • Kidd
  • Lutheran
  • Diego
  • Xg
  • P
  • Ee
  • Cc
  • MNSs

To diagnose erythroblastosis fetalis, a doctor will order a routine blood test during your first prenatal visit. They’ll test for your blood type.

The test will also help them determine whether you have anti-Rh antibodies in your blood from a previous pregnancy.

The fetus’s blood type is rarely tested. It’s difficult to test for a fetus’s blood type and doing so can increase the risk for complications.

Frequency of testing

If initial testing shows your baby may be at risk for erythroblastosis fetalis, your blood will be continually tested for antibodies throughout your pregnancy — approximately every two to four weeks.

If your antibody levels start to rise, a doctor may recommend a test to detect fetal cerebral artery blood flow, which isn’t invasive to the baby. Erythroblastosis fetalis is suspected if the baby’s blood flow is affected.

Rh incompatibility

If you have Rh-negative blood, the father’s blood will be tested.

If the father’s blood type is Rh negative, no further testing is needed.

However, if the father’s blood type is Rh positive or their blood type isn’t known, your blood may be tested again between 18 to 20 weeks of pregnancy, and again at 26 to 27 weeks. You’ll also receive treatment to prevent erythroblastosis fetalis.

ABO incompatibility

If your baby is jaundiced after birth, but Rh incompatibility isn’t a concern, the baby may be experiencing problems due to ABO incompatibility.

ABO incompatibility occurs most frequently when a mother with an O blood type gives birth to a baby who has an A, B, or AB blood type.

Because O blood types may produce both A and B antibodies, the mother’s blood can attack the baby’s. However, these symptoms are generally much milder than a Rh incompatibility.

ABO incompatibility can be detected via a blood test known as a Coombs test. This test, along with a test to determine the baby’s blood type, is performed after the baby is born. It can indicate why the baby may appear jaundiced or anemic.

These tests are usually done for all babies whose mothers have type O blood.

If a baby experiences erythroblastosis fetalis in the womb, they may be given intrauterine blood transfusions to reduce anemia. When the baby’s lungs and heart mature enough for delivery, a doctor may recommend delivering the baby early.

After a baby is born, further blood transfusions may be necessary. Giving the baby fluids intravenously can improve low blood pressure. The baby may also need temporary breathing support from a ventilator or mechanical breathing machine.

Babies born with erythroblastosis fetalis should be monitored for at least three to four months for signs of anemia. They may require additional blood transfusions.

However, if proper prenatal care and postpartum care are delivered, erythroblastosis fetalis should be prevented and the baby shouldn’t experience long-term complications.

A preventive treatment known as RhoGAM, or Rh immunoglobulin, can reduce a mother’s reaction to their baby’s Rh-positive blood cells. This is administered as a shot at around the 28th week of pregnancy.

The shot is administered again at least 72 hours after birth if the baby is Rh positive. This prevents adverse reactions for the mother if any of the baby’s placenta remains in the womb.