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In cases where there is a suspected fetal abnormality or significant fetal anemia, defined as either low blood count or low platelet count, your provider may recommend obtaining a sample of the baby’s blood while it is still in the womb.

The procedure is similar to an amniocentesis. For fetal blood sampling, the mother’s abdomen is cleansed and then ultrasound is used to identify the fetal umbilical cord. Under continuous ultrasound direction, a thin needle is introduced through the mother’s abdomen into the umbilical vein. A small (usually less than 1 milliliter) amount of blood from the baby is obtained and can be used to determine if the baby has a low blood count. The blood sample can also be used to test for genetic conditions or infection. The needle is then removed and the baby is monitored after the procedure.

When significant fetal anemia (low red blood cell count) is identified, a fetal in utero transfusion is performed. While the needle is in place, blood that has been carefully selected for specific use in the baby is then transfused into the umbilical vein. The baby is continuously monitored with ultrasound during the procedure. When the need for fetal transfusion is suspected, local anesthesia, or a spinal or epidural anesthesia may be used. The transfusion is continued until the fetal anemia is corrected, and periodic testing of the fetal blood count is done at the bedside during the procedure to ensure the correct amount of transfusion.

In rare cases, transfusion of platelets as well as red blood cells may be required. Depending on the reason for the transfusion, several transfusions may be necessary over the course of the pregnancy.