A Scottish couple have become the first in the country to undergo groundbreaking fertility screening to prevent their son being born with cystic fibrosis.

Lee and Stephen Smith were one of three couples given the IVF-style tests, which attempt to screen for single-gene disorders.

Baby Thomas was born on November 14 last year and, after a final set of tests, doctors confirmed he does not have the condition.

Stephen, 37, said when their first child, four-year-old Eden, was diagnosed with cystic fibrosis, the pair had no idea they were both carriers of the “faulty gene” which causes it.

He said: “There is no history of it in either of our families so we didn’t suspect a thing.”

The couple, from East Lothian, decided on the treatment when trying for a second child, as they said the one-in-four chance of them having another baby with the condition was too big a risk.

Lee, 40, said: “We probably spent the first three years in shock, and trying to make sure we could deal with Eden’s symptoms.

“Although she is generally quite well we have to be careful she doesn’t catch any infections, as her immune system isn’t as able to fight infection.

“Having two children with cystic fibrosis can mean they constantly keep passing infections back and forth.

“We decided we couldn’t risk our children’s health like that.

“Looking after one child who has cystic fibrosis can be tough at times, but if you had two children with the condition, trying to ensure both were kept well and didn’t cross-infect each other would be much more difficult.

“We knew we wanted another child, and were really pleased when we got the opportunity to undergo this treatment.

“We were really lucky that it worked for us first time. I was keen to get things moving as my biological clock was ticking.”

Stephen added: “We’ve been lucky in many ways because no other children at Eden’s school have cystic fibrosis, so the chance of cross-infection there is low.

“but we always wanted her to have a younger brother or sister while keeping them both as healthy as possible.”

The Western General Hospital in Edinburgh is Scotland’s only hospital to offer the pre-implantation testing, and can take up to 15 couples a year.

Around one in 25 people carries the faulty gene, but it is only when two carriers have a child together that the condition can be passed on.

There is a one in four chance that a child born from two carriers of the faulty gene will have cystic fibrosis, with a one in two chance of it being a carrier.

Pre-implantation genetic diagnosis involves the testing of embryos, created through IVF treatment, to ensure they are free of genetic conditions, before they are implanted.

Dr Mary Porteous, a consultant in clinical genetics for NHS Lothian, carried out the genetic testing for the treatment.

She said: “it is fantastic that we are able to offer this treatment for couples who are affected by single-gene defects, and I am pleased that Lee and Stephen were the first couple to benefit.

“The treatment is only offered to couples who already have an affected child.”

Cystic Fibrosis is one of the UK’s most common life-threatening inherited diseases, affecting more than 8500 people.

l The condition affects the internal organs, particularly the lungs and digestive system, by clogging them with thick sticky mucus. this makes it hard to breathe and digest food.

l Symptoms can include a troublesome cough, repeated chest infections, prolonged diarrhoea and poor weight gain.

l more than two million people in the UK carry the faulty gene that causes Cystic Fibrosis – around one in 25 of the population. If two carriers have a child, their offspring has a one in four chance of having the disease.