The next few weeks should be exciting for Bianca Sakol as she is due to give birth to her first child in January.

But it has been a long road to this point for the 29-year-old and her husband, Gary.

The couple are both carriers of Canavan disease and have twice made the traumatic decision to terminate pregnancies after discovering their unborn children had the severe disorder.

Canavan causes progressive physical and mental deterioration, with symptoms including abnormal muscle tone, seizures and rapidly increasing head circumference.

The disorder is often only detected between three and nine months and life expectancy is expected to be around the teenage years. There is no cure.

The Sakols had not been tested when Bianca first became pregnant. "We tried to make a calculated decision," Mr Sakol, 33, explained. "Was it worth paying the money considering the odds are so low? At one point we decided not. We figured that the odds meant it was so unlikely to be us."

"It just wasn't on our agenda," Mrs Sakol added. "I made an appointment and then we cancelled it because something else came up. You keep thinking it is not going to happen to you."

But after being screened while she was pregnant, the couple received the earth-shattering news. They later faced the same agony once again.

"It was horrendous and heartbreaking but at least we knew," said Mr Sakol, executive director of Habonim Dror. "We were considering the option of PGD [pre-implementation genetic diagnosis, similar to IVF] when Bianca fell pregnant for the third time. Thankfully this time the baby, while a carrier like Bianca and myself, is unaffected. We were absolutely over the moon."

His wife added: "Now I always tell people to do the screening before they are pregnant.

"Even if you would not make the same decision we did, it's better to know. People say they would never terminate - that's fine. But you need to put yourself in a position to know."

She stressed how rare it is for both prospective parents to carry the same affected gene. "It is quite isolating. We only know one other carrier couple."

Mr Sakol said: "The test itself was extremely easy and painless. We popped along to our screening centre on the day and were in and out within 30 minutes."

The Bushey residents are now looking to the future.

"I'm still nervous because that never goes away once you have been through it," said Mrs Sakol, a Jewish charity events manager. "But thank God there has been a good outcome. I feel very grateful. It's surreal but very exciting."

The couple have been heavily supported by Jnetics, who referred them to Sara Levene, principal genetic counsellor at Guy's. She helped them understand the options available.

"We will always be eternally grateful to Jnetics," Mr Sakol concluded. "They gave us the tools to make a decision that was right for us and to help prepare ourselves for the future.

"This is an incredible tool that wasn't around in our parents' day. We encourage people to make full use of it."