Rachael Casella remembers the exact moment her whole world came crashing down.

Key points: Parents and doctors say more couples need to know about pre-pregnancy genetic testing

Parents and doctors say more couples need to know about pre-pregnancy genetic testing Four out of five families who have a baby with a genetic disorder have no family history

Four out of five families who have a baby with a genetic disorder have no family history One in 20 people don't know they have the gene for SMA, cystic fibrosis or Fragile X syndrome

"On the 11th of March, 2017, we welcomed our beautiful baby girl Mackenzie and life was perfect. We were just complete," she said.

"But at 10 weeks, a lactation consultant noticed Mackenzie was floppy and not pushing her head up like other babies and told us to go to the doctor.

"We went to a GP, a paediatrician and then a neurologist and Mackenzie was diagnosed with spinal muscular atrophy type 1.

"And we asked what the cure was and they said there's no cure — it's terminal. Our world just crashed."

SMA is a rare, inherited, genetic muscle-wasting disease, characterised by a loss of nerve cells called motor neurons.

Mackenzie was 10 weeks old when she was diagnosed with spinal muscular atrophy (SMA). ( Supplied: Rachael Casella )

The disease slowly destroys the muscles in the arms and legs, as well as internal muscles that control breathing, coughing and swallowing.

"We were told eventually she'd lose the ability to breathe, and we would just have to watch it. There's nothing that we could do," Ms Casella said.

For someone to be affected with SMA, they need to have inherited an altered gene from both their parents.

The Casellas had no idea they carried the gene, sealing Mackenzie's fate the moment she was conceived.

"The thing that made us the angriest is SMA is the number one genetic killer in babies under two," Mr Casella said.

"How could we not have heard of it? Why don't they test for it — they test for Down syndrome. Why would they not test for the number one genetic disorder?"

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'One in 1,000 couples is going to have a disaster'

Rachael Casella says there was no indication that there was anything wrong with Mackenzie when she was born. ( Supplied: Rachael Casella )

A test to identify if someone carries the gene for SMA has been available in Australia since 2012, but very few people know it.

The Casellas only learned about its existence after Mackenzie was diagnosed.

"We should never have gone through this. We didn't need to go through this. No-one should feel this pain. It's preventable through carrier testing," Ms Casella said.

The simple blood or saliva test was developed by the Murdoch Children's Research Institute, and is offered by Victorian Clinical Genetic Services in Melbourne, as well as other clinics.

Mackenzie's parents had no idea she was ill until a lactation consultant noticed she couldn't hold up her head. ( Supplied: Rachael Casella )

As well as identifying SMA, it also alerts prospective parents if they carry the genes for cystic fibrosis and Fragile X syndrome — the most common cause of inherited intellectual disability.

The three-in-one test costs $385 and is not covered by Medicare, except in some cases of Fragile X syndrome.

People outside Victoria can access the test online.

But Professor Bill Ledger, head of obstetrics and gynaecology at Sydney's Royal Hospital for Women, believes all Australian couples planning a family should be informed about the test.

"More than one in 1,000 couples is going to have a disaster like this this year in Australia, so people should know about it," he said.

"They should then make their own decision about whether they want to do the screening or not.

"Not everybody will think it's the right thing to do — and that's obviously up to them."

Offering couples a choice

About one in 20 Australians carries at least one altered gene that could cause cystic fibrosis, SMA or Fragile X syndrome in their children.

The test costs $385 through the Victorian Clinical Genetic Services ( ABC News )

"One of the reasons why we started offering this testing was after lobbying from the families themselves," said Professor David Amor from the Murdoch Children's Research Institute.

"They would come to our clinics and they would say, 'Why couldn't we have found out that we were at risk of having a child who was affected before we had an affected child?'

"So we set off down this pathway of trying to offer testing that would give couples who are planning to have a child that choice."

Pregnant women are already routinely offered another test called the "non-invasive prenatal testing", which tests a mother's blood for signs of Down syndrome.

"We feel it's important to make couples aware of this three-in-one testing as well, and make sure they are fully informed," Professor Amor said.

The Royal Australian and New Zealand College of Obstetricians and Gynaecologists recommends pre-pregnancy genetic screening be offered to all prospective mothers who have a known family history of disease.

It suggests low-risk women should be "made aware of the availability of carrier screening for cystic fibrosis, SMA and Fragile X syndrome".

The college is currently reviewing its advice about pre-pregnancy genetic screening.

Royal Australian College of GPs president Dr Bastian Seidel said the college was about to roll out a new education resource for all GPs about genetic medicine, including screening.

"Expectant mothers and women planning a pregnancy should be provided with information about prenatal screening for chromosomal conditions," he said.

"GPs should support women and couples to make informed, independent decisions about the utility of prenatal testing and reproductive options."

He said it was also important to consider non-clinical issues such as costs.

'No parent should ever have to go through what we did'

Rachael and Jonny celebrated every month of Mackenzie's life, knowing she was unlikely to make it to her first birthday. ( Supplied: Rachael Casella )

After Mackenzie's devastating diagnosis, the Casellas decided to give their baby daughter as many positive experiences as possible in her short life.

"That's the only thing we could do — to give her a complete life, full of love and happiness and that meant the world to us," Ms Casella said.

Doctors told the couple the only medication available for SMA might not work and if it did, it would only extend Mackenzie's life by a couple of months.

They gave up work, and took Mackenzie on the trip of a lifetime.

"She flew all around the country. She went to zoos and aquariums and felt sand in her toes, and we just did everything we could to give her a lifetime of memories in the time that we had with her," she said

After contracting a cold at seven months, Mackenzie was rushed to hospital.

Mackenzie was just seven months old when she died. ( Supplied: Rachael Casella )

"We spent the night holding her and singing to her and telling her how much we loved her and she passed away quietly between us," Ms Casella said.

"We washed her and dressed her and we walked her down to the morgue because we didn't want anyone else to do that.

"And I share our story because no parent should ever have to go through what we went through.

"That's why we are campaigning so hard for the Australian Government to help us change this. It just shouldn't happen."

The couple will meet Federal Health Minister Greg Hunt next week to lobby for the test to become routine.

"We hope that the test is subsidised, because we want it to be equitable access for all," Mr Casella said.