Sickle cell disease is a genetic disorder in which the gene encoding for the protein hemoglobin (HBB) is mutated. This mutation causes red blood cells to become deformed or “sickle-shaped.” The deformed blood cells are unable to travel normally inside the small blood vessels, which causes pain, inflammation, and poor blood flow to different organs and tissues.
Sickle cell anemia risks associated with pregnancy
With proper prenatal care, most women with sickle cell anemia have a healthy pregnancy. However, the disease does increase the risk of complications during pregnancy. In addition, the pregnancy itself increases the frequency of vaso-occlusive crises and joint pain and inflammation for many women.
Complications can include premature birth (earlier than 37 weeks), low birth weight, and stillbirth.
Some treatments for pain or disease management, such as hydroxyurea, cannot be taken during pregnancy and this can worsen the mother’s symptoms. Patients with kidney or heart disease also may see their symptoms become worse during pregnancy.
Passing the gene causing sickle cell anemia to the baby
If either parent has sickle cell anemia or carries one mutated HBB gene, they can pass the trait or disease to their children.
There are two copies of every gene in the body; children inherit one copy of each gene from each parent. Children who inherit two copies of the mutated HBB gene will develop sickle cell anemia.
So, if both parents have sickle cell anemia — two copies of the mutated HBB gene — then their children definitely will have the disease.
If both parents have one copy of the disease-causing gene, they are “carriers” and have a one in four risk of having a child with sickle cell anemia. Inversely, they have a one in four chance of having a child unaffected by the disease and a one in two chance of having a child who also is a carrier.
Genetic testing during pregnancy
There are genetic tests available for sickle cell anemia. The partner of women who have sickle cell anemia should be tested for the presence of the mutated HBB gene to determine if they are a carrier of the disease.
Women with sickle cell anemia whose partner also is a carrier of the disease have a one in two risk of having a child affected by the disease. So, during pregnancy, women can opt to have the fetus tested for sickle cell anemia either through amniocentesis or chorionic villus sampling (CVS).
Amniocentesis is performed between weeks 15 and 20 of pregnancy. A needle is inserted through the abdomen to the womb to take a sample of the amniotic fluid, which surrounds the fetus. The amniotic fluid contains shed cells from the fetus, which can be tested for genetic abnormalities, including mutations in the HBB gene.
Chorionic villus sampling is performed earlier than amniocentesis, between weeks 10 and 13 of pregnancy. Chorionic villi are protrusions of the placenta that contain genetic material from the fetus. Samples of these protrusions can be collected using a needle inserted through the abdominal wall, or in the cervix, and tested for mutations in the HBB gene.
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