What is Fetal Anemia?

Red blood cells carry oxygen to cells and organs throughout our bodies – without them, our cells would die. Anemia happens when red blood cells are lacking in number or quality, and can’t properly nourish our cells and organs. When this happens to a growing baby during pregnancy, it is called fetal anemia.

Fetal anemia can range from mild to serious and may cause many complications. In severe cases, the baby’s heart tries to compensate for the lack of red blood cells by pumping extra hard, which can lead to fetal heart failure.

Causes of Fetal Anemia

Fetal anemia may have several causes, including:

  • Alloimmunization - This occurs when the baby inherits certain blood antigens or proteins from the father that the mother does not have. The mother’s immune system may create antibodies that attack and destroy the fetal red blood cells.
  • Infection - Several maternal infections may cause fetal anemia.
  • Blood loss - Loss of blood from the baby’s circulatory system can lead to anemia.
  • Structural abnormalities - Defects in the structure of the baby’s heart or blood vessels may contribute to anemia.

Diagnosing Fetal Anemia

Fetal anemia may be detected during pregnancy through prenatal testing. Some tests may be routine, while others may be performed to check specifically for fetal anemia.

Prenatal Ultrasound

Prenatal ultrasound can detect signs of fetal heart failure or unusual blood flow in a vessel.

Maternal Blood Testing

Maternal blood testing can detect specific antibodies that may cause anemia in the baby.


Amniocentesis can test the amniotic fluid to determine how red blood cells are breaking down in the fetal circulatory system. A needle is inserted through the mother’s abdomen to collect a sample of amniotic fluid. In most cases, an ultrasound can detect fetal anemia, so an amniocentesis is rarely needed for diagnosis.

Fetal Blood Sampling

Fetal blood sampling tests blood from the umbilical vein to look for anemia. This test is similar to amniocentesis, but the needle is guided by ultrasound into the umbilical vein.

Treating Fetal Anemia

Mercy maternal and fetal medicine specialists closely monitor and treat fetal anemia to help keep your baby as healthy as possible throughout pregnancy and delivery. In mild cases, monitoring may be all you need to ensure the anemia does not cause problems.

Fetal Blood Transfusion

If the anemia is more severe, your baby may need a blood transfusion while in the womb. This procedure is done in the hospital. The blood is transfused through a needle placed into the umbilical vein. Depending on your baby’s anemia, we may recommend additional transfusions. Your care team will discuss your treatment plan with you and answer any questions you may have.

Most newborns with fetal anemia are healthy, although jaundice is not uncommon. If your newborn has jaundice that requires treatment, Mercy’s neonatologists are ready to care for your baby with expertise and compassion. Our Neonatal Intensive Care Units offer advanced, round-the-clock care for premature or critically ill babies.

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