Blood Types in Pregnancy: What Parents Should Know

If an Rh-negative mother is carrying an Rh-negative baby, there is no Rh incompatibility. If she is carrying an Rh-positive baby, some of the baby's red blood cells may enter her bloodstream during pregnancy or delivery.

Her immune system may recognize the Rh-positive cells as foreign and produce antibodies against them. This process is called Rh sensitization or Rh alloimmunization.

Sensitization often does not cause problems during the pregnancy in which it first occurs. However, once Rh antibodies have developed, they can affect a future pregnancy with an Rh-positive baby. In some cases, sensitization can also occur early enough to affect the current pregnancy.

There is no Rh incompatibility when the mother is Rh-positive, regardless of whether the baby is Rh-positive or Rh-negative.

If an Rh-negative mother has developed Rh antibodies and is carrying an Rh-positive baby, those antibodies can cross the placenta and attack the baby's red blood cells.

If red blood cells are destroyed faster than the baby can replace them, the baby may develop anemia. Severe anemia can lead to serious complications, including heart failure or, rarely, fetal death.

After birth, continued breakdown of red blood cells can cause anemia and jaundice. Jaundice occurs when bilirubin, a substance produced as red blood cells break down, builds up in the baby's blood and tissues.

Blood type, Rh status, and red blood cell antibodies are checked as part of routine prenatal blood testing.

If an Rh-negative pregnant person has already developed antibodies that could affect the baby, additional monitoring may be needed. Doppler ultrasound can be used to evaluate blood flow in the baby's brain and help determine whether significant anemia may be present.

If severe anemia develops before birth, a specialist may give the baby a blood transfusion through the umbilical cord. In some cases, early delivery may also be recommended.

After delivery, the newborn may need treatment for anemia or jaundice. Depending on the severity, treatment may include phototherapy or a blood transfusion.

Rh sensitization can usually be prevented with Rh(D) immune globulin, often known by brand names such as RhoGAM.

Rh-negative pregnant people who have not already developed Rh antibodies are generally given Rh(D) immune globulin at about 28 weeks of pregnancy. Another dose is usually given within 72 hours after delivery if the baby is Rh-positive.

Rh(D) immune globulin may also be recommended after events that could allow fetal blood to enter the mother's bloodstream, such as certain prenatal procedures, vaginal bleeding, abdominal trauma, miscarriage, or pregnancy loss.

Rh(D) immune globulin works by preventing the mother's immune system from becoming sensitized to Rh-positive red blood cells. It does not work if Rh sensitization has already occurred.

If Rh antibodies are already present, the pregnancy will be monitored more closely to determine whether the baby is developing anemia or other complications.