For recently married Bianca Sakol, discovering that her unborn child had a severe genetic disorder was "the worst thing ever". Mrs Sakol, 28, and her husband, Gary, were identified as carriers of Canavan disease following screenings by Jnetics, a charity which tests for carriers of nine major genetic conditions affecting Jews.

Children with Canavan disease develop normally for a few months before a progressive physical and mental deterioration, which often leaves them unable to sit up or speak properly. Life expectancy does not extend beyond their teens.

Knowing what the disorder would mean for their child's quality of life, the Bushey couple decided to terminate the pregnancy. "It was the saddest and most traumatic experience," confided Mrs Sakol, an events manager for a Jewish charity.

"To find out you're a carrying couple is bad enough. I can't tell you how horrendous it is to find out once you've already become attached to a baby."

One in five Ashkenazi Jews are carriers of at least one severe genetic disorder. If partners carry the same disease, there is a one-in-four chance of them passing it on to their child. The Sakols are sharing their story in an effort to encourage more couples to be tested.

"The whole way we were in denial thinking we'd be fine," said Mr Sakol, the executive director of youth movement Habonim Dror. "But it can happen to anyone."

They had considered getting screened before their marriage, but had put it off, dissuaded more by time constraints than the subsidised £190 screening fee.

"We figured it would be a waste of time because the odds were so slim. We thought: 'What are the chances?' All I can say is thank God we did.

"As difficult and horrible as it was, I can't start to imagine what would have happened if we hadn't found out."

His wife agreed, but said she wished they had known before she became pregnant. Finding out afterwards was "like being hit by a bus. We were completely not expecting it.

"If you can prevent your baby from suffering, why wouldn't you? Why wouldn't you get tested? If it can happen to us, it can happen to anybody."

She pointed out that even if the screenings identified partners as carriers of the same disorder, there were other options for having children.

"You can have a type of IVF where they test the embryos and only put in the healthy ones, so please God one day we will have a baby."

Just under 200 people have been screened so far by Jnetics, which is working to provide the kind of comprehensive coverage available in the US and Israel. It meets half the cost of the £380-per-couple fee but has set aside a small amount for cases of hardship.

Jnetics executive director Katrina Sarig said the screening process, which involves a blood test, was supported by the London Beth Din. "The community is not generally used to paying for screenings because Tay-Sachs is covered by the NHS, but considering the huge emotional and financial cost of having a child affected by any of these conditions, people need a change in mindset.

“Just to put it in context, the cost is comparable to that of booking ballet lessons or a birthday party for a child. Screening is such an important investment – it lets us know if we are at increased risk so that we are able to manage that risk effectively for our children and future generations.”

The next Jnetics screening is on October 18 at Eden Primary, 79 Creighton Avenue, London N10 1NR. For more information, you can visit Jnetics' website.