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Prenatal Genetic Diagnostic Tests

Specific information on Screening for Cystic Fibrosis ΔF508

Cystic fibrosis (CF) is a lifelong illness that can affect all of the organs of the body.

It most often causes problems with digestion and breathing.

Intellectual ability and appearance are not impacted.

There is no cure for CF, but some symptoms can be treated.

General Questions

Cystic fibrosis and pregnancy, what should I consider?

CF is a genetic disorder caused by a gene that is passed from parent to child. Carrier screening allows a family to find out their chances of having a child with CF. If you are already pregnant, a prenatal diagnostic test allows you to find out if your fetus actually has CF or is a carrier.

What does it mean if someone is a cystic fibrosis carrier?

It takes two genes, one from each parent, for a person to have CF. If a person has only one copy of a gene for CF, they are a carrier. Carriers often do not know that they have a gene for CF.

Are some groups more at risk of being carriers?

  • The risk of being a CF carrier is higher in families with a history of CF.

  • The risk also is higher for certain racial and ethnic groups.

  • CF occurs more often in non-Hispanic white people than in other racial groups.

Carrier Screening

What are the options for carrier screening?

  • Carrier screening for genetic disorders is 100% voluntary.

  • You can choose to have carrier screening or not to have carrier screening.

  • You also may think about the timing of when to have carrier screening:

    • Before or During Pregnancy

  • If you choose to have carrier screening, testing options include the following:

    • Ethnic-based screening for groups known to be at higher risk

    • Testing for many disorders at once (expanded carrier screening)

    • Testing for just one or a few specific disorders

What else could I consider?

When considering getting a screening prior to pregnancy it is important to discuss what your plan might be based on the potential outcomes.

  • If you and a partner both tested positive, would you choose to get pregnant, or choose another method of starting a family?

  • Would you consider the risk and decide to go ahead?

If you are currently pregnant what would you plan for based on learning the information, with the understanding that no Diagnostic test is 100% accurate?

  • Would you consider further testing?

  • How do you imagine this information might impact your relationship with the baby you are already carrying?

  • Would you do anything different based on the outcomes of a test?

When should I have carrier screening?

Carrier screening can be done before pregnancy or during pregnancy.

  • If you have carrier screening before you get pregnant and both you and your partner are carriers, you have more options and information.

Who can be screened for cystic fibrosis?

Carrier screening for CF is offered to all families who are thinking about getting pregnant or who are already pregnant. It is your choice whether to have this screening.

What does carrier screening for cystic fibrosis involve?

You will be asked to give a sample of blood, saliva, or tissue from the inside of your cheek.

  • Who should be tested first, me or my partner?

    • If neither partner has a history of CF then you can decide who gets tested first, otherwise, the partner with a family history could get tested first.

    • If you are already pregnant, you and your partner can be tested at the same time.

How do I make decisions about carrier screening?

Your care provider, partner, and support system can help you choose the approach that addresses your concerns and also meets current recommendations for carrier screening.

Carrier Screening Results

I'm Negative, what now?

A negative result means that your chance of being a CF carrier is small, however no screening test checks for every known CF mutation. Therefore even if your test result is negative, there still is a very small chance that you could be a carrier of a mutated gene that was not detected. If you have a negative test result but a family history of CF, you also may be tested for the specific mutation in your family if that information is available.

I’m Positive, what does this mean?

If your test result is positive, it means that you are a CF carrier. The next step is to test your partner. Both partners must be CF carriers for a fetus to have CF.

  • If your partner has a negative test result, the chance that the fetus will have CF is small.

What does it mean if BOTH partners test positive?

If both partners are CF carriers, there are three possible outcomes:

  • 50% or (1-in-2) chance the baby will be a carrier, like you and your partner. Being a carrier usually will not affect the health of the baby, but he or she could be a carrier or have a child with CF in the future.

  • 25% or (1-in-4) chance that the baby will not have CF and will not pass on the disease to future children.

  • 25% or (1-in-4) chance the baby will have CF.

Should I tell my family if I am a carrier?

It is entirely up to you with whom you share this information, however, if you have siblings who are thinking about starting families you might consider telling them you were a carrier.

Fetal Testing Options

Is it possible to find out if a fetus has cystic fibrosis?

Testing can be done to learn if a fetus has CF or is a carrier. This is called prenatal diagnostic testing. This testing can be done as early as 10 weeks of pregnancy.

How is prenatal diagnostic testing done?

  • Prenatal diagnostic tests to detect CF and other disorders include amniocentesis and chorionic villus sampling (CVS).

    • Amniocentesis usually is done between 15 and 20 weeks of pregnancy, but it also can be done up until you give birth. A very thin needle is used to take a small sample of amniotic fluid for testing. The cells are studied to detect the presence of the CF gene.

    • CVS is done between 10 and 13 weeks of pregnancy. A small sample of tissue is taken from the placenta. The cells are then checked for the presence of the CF gene.

What are there risks for both amniocentesis and chorionic villus sampling?

  • A full list of outcomes should be provided by the medical provider performing these tests.

  • You can ALWAYS ask if they are not provided.

Amniocentesis usually is done in an office or medical center. The procedure is done using a very thin needle that is inserted through the abdomen (belly) and into the uterus. An ultrasound exam is used to guide the procedure. A small sample of amniotic fluid is withdrawn from the sac surrounding the fetus. This fluid contains cells that have been shed by the fetus and are sent to a lab for testing.

  • Risks of amniocentesis include:

    • a chance of miscarriage (about 1 in 900 procedures, approx .1%) (3)

    • leakage of amniotic fluid and slight bleeding, which should stop on their own

    • transmission of blood-borne infections such as hepatitis B, hepatitis C, or human immunodeficiency virus (HIV) from the placental parent to the fetus

Chorionic villus sampling (CVS) is the primary alternative to amniocentesis. In this procedure, a sample of tissue is taken from the placenta. The main advantage of CVS is that it can be done earlier, between 10 and 13 weeks of pregnancy.

  • Risks of CVS include:

    • risk of miscarriage (about 1 in 455 procedures, approx .2%) (3)

Can I have diagnostic testing if I am using IVF?

For people using in vitro fertilization (IVF) to get pregnant, there is another testing option called preimplantation genetic testing. Before an embryo is transferred to a uterus, it can be tested for CF and certain other genetic disorders. The only embryos transferred are those that do not test positive for the disorders.

Final Thoughts

What do diagnostic test results mean?

The results of these prenatal tests can tell you with a high degree of certainty whether the fetus has CF or is a CF carrier. No diagnostic Test is 100% accurate. The results cannot tell you how severe the disease will be if the fetus has the disorder.

What are my options if my fetus has cystic fibrosis?

There is no cure for CF. If you find out that your fetus has CF, you have options:

  • You may choose to continue the pregnancy and prepare for a child with CF. You 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.

  • Another option is to end the pregnancy. You also may want to discuss the decision with any partners, a counselor, close family, or friends.

If both partners are carriers. What does this mean for future pregnancies?

If tests show that both partners are carriers, it means that in each pregnancy the fetus will have a 1-in-4 chance of having CF. If you want to know whether your fetus has CF, you will need to have amniocentesis or CVS in each pregnancy.

If you are thinking about having children in the future, you have several options:

  • You can accept the level of risk and get pregnant.

  • You may choose to have prenatal diagnostic testing in each pregnancy, or you may not.

  • You can choose not to have children.

  • You can adopt.

  • You can use donor sperm or donor eggs, but the donor should be screened for CF.

  • You can use IVF with your own sperm and eggs, and then use preimplantation genetic testing to see if the fertilized egg has CF or is a CF carrier.

You can discuss these options with family, friends, your care provider, or your genetic counselor when you are considering future pregnancies. If you are a carrier and have a new partner for another pregnancy, you can also consider testing the new partner.

*This information about carrier screening, amniocentesis, and CVS is applicable to testing for other genetic anomalies.

Adapted from information provided by the American College of Obstetricians and Gynecologists:

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