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Optional Tests: Cystic Fibrosis

Cystic Fibrosis Screening

One of the optional tests during pregnancy is screening for cystic fibrosis.  This is a blood test that is drawn from the mother.  The blood is tested to see if the mother is a carrier of the gene for cystic fibrosis.

What is Cystic Fibrosis?

Cystic Fibrosis (CF) is a disease that causes thick mucus in the lungs and digestive tract.  The thick mucus in the lungs cause lead to infections such as pneumonia.  In the digestive tract, the mucus interferes with the breakdown and absorption of food.

CF is a genetic disease and a person must receive this gene from both parents.  This gene occurs more often in people of Northern and Western European, Ashkenazi Jewish, and Northern European Caucasian descent.  Although it is not as common, CF gene can be present in people of any ethnic group including, Hispanic, African American and Asians.

When is this test performed?

The test is usually performed early in pregnancy or in the first trimester.  When the test is done early, it allows for further testing to be completed if needed.  However, the test can be done at any point of the pregnancy.

What does a negative result mean?

The CF Screening test looks for the most common mutations of the gene but does not test for all mutations.  If your result is negative, it means that the mother is most likely not a carrier of the gene.  Therefore, the baby’s risk for having CF is significantly low.

What does a positive result mean?

It means that the mother is a carrier of the gene.  The father will also need to screened.  If the father is negative, the baby’s risk for CF is significantly low.  If the father is also positive and is a carrier of the gene, the baby will have a 25% chance of having CF.

What happens if both the mother and father are positive?

If testing shows a positive result for both parents, the baby will have a 25% chance of having CF.  Knowing these results in advance can allow parents time to prepare and discuss this with their chosen pediatrician.  The hospital staff should also be aware so they can have additional staff on hand to assist the newborn to breathe, if necessary.

Also, you may consider other tests that can detect and give accurate diagnosis of the fetus early. Tissue from the placenta or the amniotic fluid around the baby can be tested to see if the fetus has a complete set of the CF gene.  Both of these tests have risks for miscarriage.

    • CVS (chorionic villus sampling) is done between 10 -13 weeks of pregnancy

A sample of placental tissue is obtained with a thin needle either through the abdomen or through the vagina and cervix. Miscarriage occurs 1 in 200.


    • Amniocentesis is done between 15-20 weeks of pregnancy

A sample of the amniotic fluid around the fetus is obtained with a needle through the abdomen.  Miscarriage occurs 1 in 400.