Many obstetricians offer prenatal screening for CF. Because CF patients inherit one CFTR gene from their mother and one from their father, for CF to present, both CFTR genes must be abnormal. The mother’s blood is first tested to see if she carries any of the gene mutations that cause CF. If she has two normal CFTR genes, then the baby will not have CF (even though the baby might inherit an abnormal CFTR gene from his or her father). If mother carries a CFTR mutation, then the father’s blood will also be tested. If he is also a carrier of a CFTR mutation, then the baby has a 25 percent chance of having CF. This would occur by inheriting two abnormal CFTR genes, one from the mother and one from the father. If both parents are found to be carriers of CFTR mutations, amniocentesis will be offered to determine if the baby has CF. Amniocentesis is usually done between 15 and 18 weeks of gestation; chorionic villus sampling can be performed even earlier in the pregnancy. If parents elect not to undergo amniocentesis, the baby should be tested for CF as a newborn.
Inheritance pattern of normal (N) or mutated (M) CFTR genes from parents who carry an abnormal copy of the CFTR gene.
