Research shows one in 20 people carry a gene for either cystic fibrosis, fragile X syndrome and spinal muscular atrophy.

There are calls for routine genetic screening of all couples planning a family, with new research showing one in 20 people carry a gene for one of three life-threatening yet rare genetic disorders.

Researchers at the Murdoch Children's Research Institute screened about 12,000 people for cystic fibrosis, fragile X syndrome and spinal muscular atrophy.

Investigator Dr Alison Archibald - who works as a genetic counsellor at the Victorian Genetics Services - says they found that it is really common for anybody to be a carrier for one of these conditions.

"You really don't need a family history to be a carrier and the affected pregnancy rate is very similar to that of Down syndrome," said Dr Archibald.

The screening showed 88 per cent of the participants had no family history of the condition and that one in 240 couples had an increased risk of having a child with these conditions.

Approximately one in 1000 pregnant women screened had a child born with one of these conditions.

This rate is comparable to the incidence of Down syndrome and health professionals should think about offering genetic screening more routinely to their patients, says Dr Archibald.

"Particularly for couples planning a pregnancy so they can find this out before they go down the path of pregnancy and they can then think about this information to inform their decision making about having a family and what options they choose," she said.

FREQUENCY OF CARRIERS AND BABIES BORN WITH CYSTIC FIBROSIS, FRAGILE X AND SPINAL MUSCALR ATROPHY.

Cystic Fibrosis (CF)

* 1 in 25 carry gene
* 1 in 2500 babies born with CF

Fragile X Syndrome (FXS)

* 1 in 250 carry gene
* 1 in 4000 babies are born with FXS

Spinal Muscular Atrophy (SMA)

* 1 in 40 carry gene
* 1 in 6000-10,000 babies born with SMA

(Source Murdoch Children's Research Insitute)