Important: This is intended as general information only. It may not apply to your specific situation. It is not a substitute for medical advice. If you have a question or concern, please raise it with me at your next appointment or contact me sooner if it's urgent.
Testing for Cystic Fibrosis
At your first pregnancy visit you will be offered a test to see whether you carry the gene that causes cystic fibrosis (CF). This test is optional – you do not have to have it done if you do not wish to.
Cystic fibrosis is one of the most common genetic diseases in our population. It is a severe disease that mostly affects the lungs, causing a build up of thickened mucous. This mucous can block the airways and trap bacteria causing a chronic cough and recurrent infections. Over time, these blockages and infections damage the lungs resulting in difficulty breathing. It also affects the pancreas which can make it difficult for sufferers to digest food. As a result, people with CF may suffer from malnutrition and poor growth. Treatment has improved over the years and many people with the disease lead full and productive lives. Nonetheless, it remains a serious disease requiring treatment on a daily basis and some people with the disease may go on to require a lung transplant. The average life expectancy for someone with CF is reduced at 35-40 years.
In order to have CF, a person needs to have two copies of an abnormal gene – they inherit one from each parent. About 1 in 25 people in the Caucasian population have one copy of the abnormal gene and are known as ‘carriers’. Carriers usually have no symptoms and are unaware that they have abnormal gene. If both parents are carriers, there is a possibility that their baby could inherit two copies of the abnormal gene and end up with the disease. Bear in mind that not all children born to two carriers will have cystic fibrosis as each parent gives one gene only (either their normal or abnormal gene) and there is only a problem for the baby if he or she ends up with two copies of the abnormal gene. In the situation where both parents are carriers, there is a 1 in 4 chance that their child will have CF. While people from other races can carry the abnormal gene, it is much less common than in Caucasians.
If you chose to have testing, you will have a DNA test performed to see if you are a carrier of the abnormal gene. If you are not, no testing of your partner is required - there is only a problem if both parents carry the gene. If you are found to be a carrier, we then test your partner to see if he carries the gene as well. If he does not carry the gene, you baby is not at risk of CF and no further testing is required.
If we find that both you and your partner carry the CF gene, we know that there is a 1 in 4 chance that your baby will have CF. If you wish, you can then go on to have genetic testing of your unborn baby to see if he or she carries the gene. This is usually done by amniocentesis.
We offer you this test so that, if you found out you were going to have a baby with cystic fibrosis, you would have the option of terminating the pregnancy. Of course, this is not a decision that you need to make before having the test and, at each step of the process, I would discuss all the options with you in detail. However, if you are certain that you would not consider a termination of pregnancy if you found out you were having a baby with CF, it’s probably best not to have the test in the first place – it’s just one more thing to worry about and one more thing to pay for! Because this is a relatively common disease, I find that many patients know or have known someone with CF and their feelings about the disease are very influenced by that person’s experience. There is no right or wrong decision with this test. It’s a very personal decision and it’s completely up to you whether you have testing or not.
Previously, CF carrier testing has been offered as a single test as a cheek swab. More recently, a blood test has developed that allows for testing of CF carrier status along with testing for carrier status of Fragile X Syndrome (a form of inherited developmental disability) and Spinal Muscle Atrophy (hereditary muscle weakness). While these other two conditions are less common in our population than CF, they are common enough to warrant offering testing, especially as this can be done easily along with CF testing for very little extra cost. It's still possible to have testing for CF only if you prefer.