Cystic Fibrosis

Prenatal Screening and Diagnosis

Cystic fibrosis (CF) is a genetic disorder that causes problems with breathing and digestion. It is caused by an abnormal gene that is passed from parent to child. There is no cure for CF, but it can be treated. Testing can be done to see if a person carries the gene and if there is a risk of passing it on to a child. This article explains:

• Cause, symptoms and treatment of CF
• Risk factors
• Testing options

What is Cystic Fibrosis?

Cystic fibrosis is a lifelong illness that can affect all of the organs of the body. It often causes problems with digestion and breathing. It does not affect a person’s looks or mental ability. In some cases, CF poses a serious risk to a person’s health and shortens life span. Despite their physical problems, many people with CF attend school, have careers, and lead full lives.

CF usually is diagnosed in the first few years of a child’s life. But, if CF is mild, it can be diagnosed later in life.

The Cause of Cystic Fibrosis

Cystic fibrosis is a genetic disorder caused by an abnormal gene that is passed from parent to child. For a recessive disorder, such as cystic fibrosis, both parents must carry a copy of the abnormal gene for the problem to occur in their child. A person who has one copy of an abnormal gene for a recessive disorder is a carrier for that disorder, even though he or she may show no signs of it. If both parents are carriers, each of their children has a 25% chance of having the disorder. Put another way, this couple has a 1-in-4 chance of having a child with CF.

Symptoms of Cystic Fibrosis

The symptoms of CF can vary in type and severity. Many people with CF produce a thick, sticky mucus in their bodies. This mucus builds up and clogs the lungs, which makes it hard to breathe, and can lead to infection. It also can affect the digestive organs, making it hard for the body to break down and absorb food. Most males with CF are sterile and cannot father children.

Treatment of Cystic Fibrosis

New drugs and treatments have improved the outlook for people with CF. But, CF is still a lifelong disease. To treat lung problems, most children wtih CF need to have physical therapy for about a half hour every day. This therapy helps clear mucus from the lungs. It is easy to do and can be done by parents or other family members.

Risk Factors

The risk of being a CF carrier is higher in certain races and ethnic groups. It occurs more often in white people than in other racial groups. The risk also is increased in families with a history of CF.

Testing for Cystic Fibrosis

Carrier testing can be done to find out if a person has a copy of the CF gene. The test is done on a blood sample.

Carrier testing can be done for couples planning a pregnancy to assess their risk. Carrier testing also is available to all pregnant women. If testing shows that a couple is at high risk, most testing can be done during pregnancy to see whether their baby will have CF.

Couples can choose to test one partner, then the other if one is a carrier, or both partners may be tested at the same time. During pregnancy, screening both partners at the same time can be helpful if the couple thinks they might be at high risk and would consider further  prenatal testing to see if the fetus has CF.

The decision to be tested is a personal one. Factors to consider are the level of risk and how the results will affect further decisions.

Test Results

One Partner Normal

If your test results are normal, the chance that you are a CF carrier is small. There are some rare CF gene defects that the test does not detect. For this reason, you could be told your test result is normal, and you could still be a carrier. The likelihood of this is very small.

One Partner Positive

If the test shows that one partner is a carrier, the next step is to test the other partner. Both parents must be CF carriers for the baby to have CF.

If one parent has a normal test result, the chance that the baby will have CF is small. Because the risk is small, if one partner is a carrier but the other has a normal result, no further testing is recommended. If the father is not available for a carrier test, a genetic counselor may be able to help you decide whether to have prenatal testing.

Both Partners Positive

If two people who are both CF carriers have a baby, there is a 25% chance that the baby will have CF. However, it is more likely that the baby will be a carrier, like the parents, and will have the gene but will not have the disease. It also is possible that although the parents are both carriers, the baby will not be a CF carrier.

If CF testing shows that both parents are carriers, genetic counseling may be useful. The genetic counselor can give you more information and help you decide if you want to test the developing baby for CF. Couples also may want to share this information with family members to help them plan their pregnancies.

Follow-up Tests

If both partners are CF carriers, further prenatal testing can be done to see if the baby CF. This testing is not recommended when only one partner is a carrier. Parents may want to know if the baby will have CF so that they can prepare for the care of a child with special health care needs, or they may choose to end the pregnancy.

Prenatal tests done to detect CF and other disorders are chorionic villus sampling (CVS) and amniocentesis. Chorionic villus sampling can be performed after 9 completed weeks of pregnancy. A tiny piece of the placenta is removed and sent to a lab. It is grown in a culture fro about 7 days. The cells are then checked for the presence of the abnormal CF gene.

Anmiocentesis is performed at 15-20 weeks of pregnancy. A needle is used to take a small sample of amniotic fluid from around the baby that contains some of the baby’s cells fro testing. In the lab, the baby’s cells from the amniotic fluid are grown in a special culture. This usually takes about 10-12 days. Next, the cells are studied to detect the presence of the abnormal CF gene.

For couples who are using in vitro fertilization to become pregnant, there is another testing option. Tests can be done on the fertilized egg to check whether the CF gene is present. This test is called preimplantation genetic diagnosis because it occurs before the fertilized egg is implanted in the mother’s uterus.

The results of these prenatal tests are highly accurate. However, they cannot always tell you how severe or mild the disease will be, if the baby has the disorder. Even when both parents are CF carriers, there is a 75% chance that the test results will show the baby does not have CF.

Your Choices

There is no cure for cystic fibrosis. There are two choices when it is found that a developing baby has CF.

1. Continue the pregnancy and prepare for a child with CF. Couples can use this time to learn as much as possible about the disease, current treatment options, and the experiences of other families who have a child with CF.
2. End the pregnancy. Each state has its own laws on pregnancy termination. You should discuss this decision with your doctor. Yo also may want to talk with your partner, counselors, and close friends.

Resources are available to help you learn more about CF and your chances of having a baby with CF. Although there is no cure for CF, research on more effective treatments is under way.