What is the cause of sickle cell anemia in fetus?

You may be confused.: Fetuses do not suffer from sickle cell anemia in utero because they have a different type of hemoglobin (fetal) that is unaffected even in individuals destined to have sickle cell disease later in life. Affected fetuses come from affected or carrier parents and sickle cell disease is a genetic condition without cure at present. See a genetic counselor to discuss these issues in detail.

Defective genes: The chromosomes contain genes which have the instruction on how the work of the body is done. In SS disease, each parent has given the fetus a defective gene, so defective blood cells would be made after baby is born & becomes an air breather. Before then its red cells are made using other instructions. The parents are unaffected because each has one normal gene that can make good blood cells.