Screening for CF, by analysis of cells taken from a mouthwash, has become possible since the faulty gene was located.
Cystic fibrosis is an inherited disorder that affects about 8,000 people who rarely survive beyond middle age. It is a recessive gene disorder so when two carriers have children there is a one in four chance of the child being affected.
Two studies in tomorrow's edition of The Lancet show that not all partners of women screened for the disease agree to be screened themselves, and that national screening of adults might only detect between half and three quarters of couples at risk of having babies with cystic fibrosis.
The current screening procedure costs about pounds 30,000 for 10,000 tests and a cystic fibrosis child about pounds 5,000 a year to care for. But a leader in The Lancet cautions that national screening may not be beneficial because of the emotional cost to couples who may decide to have terminations or to have no children at all.
One study of 3,176 people from Watford, carried out by Bob Williamson, professor of biochemistry and molecular genetics at St Mary's Hospital Medical School, London, found 100 carriers, 87 of whose partners agreed to be screened as well.
In a separate study of 3,165 pregnant women in Edinburgh, one in 29 were carriers. Four women had partners who were carriers and one pregnancy was affected and terminated.