Cystic fibrosis (CF) is a genetic disease caused by a specific mutated gene. Since we know which gene is responsible, it is possible to diagnose CF in an unborn child through prenatal genetic testing but it can’t be done with a simple blood test. In order to find out if your baby has CF, you’ll need to have more invasive tests.
Who Should Be Tested?
Genetic testing for cystic fibrosis is not part of routine prenatal care. Since the tests are invasive, they do carry some risk and it’s not necessary to test everyone across the board. So who should be tested?
You should be tested if:
- You and your partner are both CF carriers, even if you have different mutations
- One parent is a carrier and the other has cystic fibrosis
You don’t need to be tested if:
- Only one parent is a CF carrier, because your baby will not have CF
- Both parents have CF, because your baby will have CF
What Will the Test Tell Me?
Prenatal genetic testing will tell you if your child has -– or carries -- cystic fibrosis, but it will not tell you how severe or mild his disease will be.
How Prenatal Genetic Testing Is Done
To find out if your baby has cystic fibrosis, your doctor will need to collect some cells that contain your baby’s genetic material. In most cases, the cells can be collected in two ways – chorionic villus sampling and amniocentesis. If your baby was conceived through in vitro fertilization, genetic testing can be done on the fertilized egg before it is implanted. Once the cells are collected they are sent to a lab, grown in a culture, and then examined to see if they contain the genetic defect that causes CF.
Chorionic Villus Sampling Versus Amniocentesis
Chorionic villus sampling and amniocentesis are similar procedures. Both are done in an examination room. You will be awake, but may be given a local anesthetic. Throughout the procedure, your doctor will use ultrasound to keep an eye on your baby and to help guide the needle or catheter as it enters your uterus to remove cells for testing. There are some important differences though.
Chorionic villus sampling: Can be done after the ninth week of pregnancy. Either a thin tube is inserted through the vagina and cervix, or a needle is inserted through the abdomen. A very small piece of placenta is collected and sent to the lab for testing. Results usually take about a week.
Amniocentesis: Done between 15 and 20 weeks of pregnancy. A needle is inserted through the abdomen to withdraw a small amount of amniotic fluid that is sent to the lab for testing. Results usually take between 10-12 days.
American College of Obstetricians and Gynecologists. 2009. Cystic Fibrosis Prenatal Screening and Diagnosis. 10 August 2009.