Screening for Cystic Fibrosis in Pregnancy

Cystic fibrosis (CF) is a disease that affects a person’s lungs, digestive system, and reproductive systems. It can lead to thickened secretions, which can result in recurrent lung infections, digestive issues, and infertility. CF is genetic, which means that it runs in families and can be passed from parents to their children. People with CF live to an average of 37 years of age (though a rarer, milder form exists, and those people tend to live into their 50s). The most common cause of death is respiratory failure.

Because we know many of the genetic mutations on the gene that causes it, doctors can screen pregnant women for CF. In terms of passing it to children, CF is autosomal recessive. This means that both parents must have the gene for CF to pass it to their children. Because it is recessive, a person can carry the CF gene without actually having the disease. When both parents are carriers, each child they have together has a 25 percent chance of having CF, and all the rest will be carriers.

Being a carrier for CF is relatively common, and it varies based on ethnicity. One out of 25 Caucasians is a carrier, while only one out of 94 Asian Americans is. Keep in mind that a woman who is a CF carrier can only have a child with CF if her partner is also a carrier—and even then, about 75 percent of the time, their child will not be affected with CF. Overall, approximately only one in 2,500 Caucasians have CF.

Genetic screening for CF can help put a woman’s mind at ease when she screens negative for the mutation. Negative screening means it is impossible for her baby to have CF. Because being a carrier for CF is very common, this test is routinely offered to all pregnant women. This test can be done after a woman finds out she is pregnant or as part of preconception genetic testing done when a woman is not yet pregnant but planning to start trying.

The test involves drawing a woman’s blood and screening for the mutated CF gene. If she doesn’t have it, the screening is done. If she does have it, then the partner should be tested. If the partner also has a mutation, the couple is usually referred to a genetics counselor to discuss further testing options, which may include chorionic villus sampling or amniocentesis to be able to screen and diagnose the baby.

Choosing whether or not to have CF genetic testing is a personal one. Some women would opt to not continue their pregnancy if they knew their developing baby had CF, while others would continue the pregnancy but would want the time to prepare for raising a child with a chronic, life-threatening disease. Discussing screening with your doctor or midwife can help you determine if CF screening is right for you.

Sources:

• The American College of Obstetricians and Gynecologists
• Committee Opinion #486: Update on carrier screening for cystic fibrosis
• April 2011.
  The American College of Obstetricians and Gynecologists
• FAQ #171: Cystic fibrosis—prenatal screening and diagnosis.

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