Cystic Fibrosis Screening Is Now Recommended

By: Bradley G. Goldberg, M.D.

Since late in 2001, The American College of Obstetricians and Gynecologists (ACOG) now recommends that OB/GYN physicians make Cystic Fibrosis DNA screening (a blood test) available to all patients. Although this screening test should be available to all patients, it should be specifically offered to Caucasian couples who are planning pregnancy, or who have recently become pregnant, although other ethnic groups may also wish to consider it as well.

This is an ACOG recommendation that is a result of the research that has been done with The Human Genome Project. This was an enormous research project performed by several scientists all over the world to identify the location of all of the genes in the human body.

Cystic Fibrosis is a disease that affects both the lungs and the digestive tract. Therefore it can cause problems with nutrition and breathing. It does not affect intelligence or appearance. Lifespan is decreased with the average Cystic Fibrosis patient living only to the age of around 30, although with proper treatment some people may live longer. Prior to this new DNA screening test, people who have this disease were not usually diagnosed until between the ages of 1-3 years old.

In the Caucasian population the chance of being a carrier of this condition is 1 in 29. This is even if no one in your family has a history of the disease. The condition is much less common in Asian, African-American, and Hispanic populations. In addition, the screening test is not as accurate in these populations either. This is why ACOG only recommends the test for Caucasians, although certainly other ethnic groups could have the test performed if they so desire.

Cystic Fibrosis is a recessive genetic disorder. This means that both parents must be carriers for the child to be affected. Therefore, for patients who desire testing I recommend screening as follows: First, the mother is screened. If her test is negative, then no further testing is necessary. If her test is positive, then the father should be screened as well. If the father’s test is negative, then there is almost no chance that the baby could be affected.

If both the father and the mother test positive as carriers, then there is a 25% chance that the baby would be affected. Looking at it another way, there is a 75% chance that the baby will be healthy and unaffected even if both parents are carriers. The only way to tell for sure if the baby will be affected is to perform an amniocentesis. This is a procedure where a small amount of the amniotic fluid that surrounds the baby is removed and tested.

Some drawbacks about screening include that the test has a 20% false negative rate. This means that even if you have a normal test you still might be a carrier (20% are missed). In addition, if both parents screen positive and the amniocentesis is performed proving that the baby will have Cystic Fibrosis disease (25% chance), there is currently no treatment available to change that. Therefore it serves mainly to alert the parents and pediatritian that this problem exists. Since Cystic Fibrosis DNA screening is a relatively new testing recommendation, some insurance companies will not cover these lab charges which currently average around $300. Due to these drawbacks not everyone choses to have the test performed. However, if you do desire this screening it is best done early in the pregnancy, or even before pregnancy
 

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