Sickle Cell Disease

What is sickle cell disease?

Sickle cell disease is an inherited blood disorder characterized by defective hemoglobin (a protein in red blood cells that carries oxygen to the tissues of the body).

Sickle cell disease involves the red blood cells, or hemoglobin, and their ability to carry oxygen. Normal hemoglobin cells are smooth, round, and flexible, like the letter "O," so they can move through the vessels in our bodies easily. Sickle cell hemoglobin cells are stiff and sticky, and form into the shape of a sickle, or the letter "C," when they lose their oxygen. These sickle cells tend to cluster together, and cannot easily move through the blood vessels. The cluster causes a blockage and stops the movement of healthy, normal oxygen-carrying blood. This blockage is what causes the painful and damaging complications of sickle cell disease.

Sickle cells only live for about 15 days, while normal hemoglobin can live up to 120 days. Also, sickle cells risk being destroyed by the spleen because of their shape and stiffness. The spleen is an organ that helps filter the blood of infections and sickled cells get stuck in this filter and die. Due to the decreased number of hemoglobin cells circulating in the body, a person with sickle cell disease is chronically anemic. The spleen also suffers damage from the sickled cells blocking healthy oxygen carrying cells. Without a normal functioning spleen, these individuals are more at risk for infections. Infants and young children are at risk for life-threatening infections.

What causes sickle cell disease?

Sickle cell disease is inherited. It is the result of a genetic mutation that causes hemoglobin cells to be defective. This mutation is thought to have originated in areas of the world where malaria was common, since people with sickle trait do not get malaria. The sickle trait actually offers some protection from the parasite that causes malaria, which is carried by mosquitoes. Malaria is most often seen in Africa and in the Mediterranean area of Europe.

Sickle cell disease primarily affects those of African descent and Hispanics of Caribbean ancestry, but the trait has also been found in those with Middle Eastern, Indian, Latin American, Native American, and Mediterranean heritage. In the US, it has been estimated that 1,000 children are born each year with sickle cell disease. One in twelve African-Americans has sickle cell trait.

A baby will be born with sickle cell disease only if two sickle cell genes are inherited - one from the mother and one from the father. A person who has only one sickle cell gene is healthy and said to be a carrier of the disease. They may also be described as having sickle cell trait. A carrier has an increased chance to have a baby with sickle cell anemia. Once parents have had a child with sickle cell disease, there is a one in four, or 25 percent, chance with each subsequent pregnancy, for another child to be born with sickle cell disease. This means that there is a three of four, or 75 percent, chance for another child to not have sickle cell disease. There is also a 50 percent chance that a child will be born with sickle cell trait, like the parents.

The birth of a child with sickle cell anemia is often a total surprise to a family, since many times there is no previous family history of sickle cell disease. Since both parents are healthy, they had no prior knowledge that they carried the gene or were at risk for passing the gene on to a child.

How does pregnancy affect sickle cell disease?

Some women have no change in their disease during pregnancy. However, sickle cell crises (painful events) may still occur in pregnancy and may be treated with medications that are safe to use during pregnancy. Pre-existing kidney disease and congestive heart failure may worsen during pregnancy, even with proper treatment.

How does sickle cell disease affect pregnancy?

The risks for pregnancy depend on whether the mother has sickle cell disease or sickle cell trait. Generally, women with sickle cell trait are not at increased risk for problems, however, they may experience frequent urinary tract infections. It is also important to remember that, unlike sickle cell anemia, a woman with sickle cell trait can have iron deficient anemia while pregnant and may need iron supplementation for this reason.

The ability of the blood cells to carry oxygen is especially important in pregnancy. The sickling and anemia may result in lower amounts of oxygen going to the fetus and slowed fetal growth. Because sickling affects so many organs and body systems, women with the disease are more likely to have complications in pregnancy. Complications and increased risks for the mother may include, but are not limited to, the following:

• infection, including urinary tract (especially kidney) and lungs
• gallbladder problems including gallstones
• heart enlargement and heart failure from anemia

Complications and increased risks for the fetus may include, but are not limited to, the following:

• miscarriage
• intrauterine growth restriction (poor fetal growth)
• preterm birth (before 37 weeks of pregnancy)
• low birthweight (less than 5.5 pounds)
• stillbirth and newborn death

How is sickle cell disease managed in pregnancy?

Although expectant mothers with sickle cell trait are not at higher risk for pregnancy complications, the baby may be affected if the father also carries the trait. Testing of the baby's father is recommended prior to pregnancy, or at the first prenatal visit. If the baby's father has sickle cell trait, amniocentesis (a procedure used to obtain a small sample of the amniotic fluid) or other methods of prenatal diagnosis may be offered to help determine if the fetus has the trait.

Early and regular prenatal care is important for pregnant women with sickle cell disease. More frequent prenatal visits allow for close monitoring of the disease and of fetal well-being. General pregnancy care includes a healthy diet, prenatal vitamins, folic acid supplements (a B vitamin), and preventing dehydration.

Some women may benefit from blood transfusions to replace the sickled cells with fresh blood. These may be done several times during the pregnancy to help increase the blood's ability to carry oxygen and decrease the number of sickled cells. It is important for women who receive blood transfusions to be screened for antibodies that may have been transferred in the blood and that may affect her fetus. The most common antibodies are to the blood factor Rh.

Fetal testing may begin in the second trimester and include:

• ultrasound (to measure fetal growth)
• nonstress test - measures fetal heart rate in response to fetal movement.
• biophysical profile - a test that combines an ultrasound with the nonstress test.
• Doppler flow studies - a type of ultrasound which use sound waves to measure blood flow.

During labor, intravenous (IV) fluids are given to help prevent dehydration. Most women will receive extra oxygen through a mask during labor and a fetal heart rate monitor is often used to watch for changes in heart rate and signs of fetal distress. There are no special recommendations for the type of delivery for women with sickle cell disease and most women can deliver vaginally, unless there are other complications.