The Thai surrogate mother of baby Gammy says she is shocked to learn that the child's biological father is a convicted paedophile.

West Australian electrician David John Farnell, 56, was sentenced to three years' jail in 1997 for sexually molesting two girls under the age of 13.

Just months later, while still imprisoned, he was charged again - this time with six counts of indecent dealings with a child under the age of 13.

Those offences were said to have occurred over a 10-month period in the mid-1990s.

Farnell was found guilty a second time and received an 18-month jail term.

Thai surrogate mother Pattaramon Chanbua, 21, has accused the man and his wife of abandoning their Down syndrome son, known as baby Gammy.

The couple denies knowing about the boy and says doctors only told them about his healthy sister, who they brought home to Australia.

When told of Farnell's child sex convictions on Tuesday, Ms Chanbua said she was shocked by the news.

"I was startled and worried," she said. "Right now I am still worried."

When asked if she wanted the baby girl to be brought back to Thailand, she replied: "That would have to be up to the law."

Western Australia's Department for Child Protection says it is assessing the "safety and wellbeing" of the baby girl in Australia.

Two DCP officers visited the family's home on Monday evening. The family was not home but it is understood the officers left contact details.

Parents 'definitely knew' about Gammy

A former employee of the surrogate agency who was the go-between dealing with the biological parents and the surrogate mother told 7.30 there was confusion about what to do with Gammy once they realised he had Down syndrome.

"Nobody knew what to do," she said.

"If they decided to abort one baby what about the other one? Nobody could guarantee you will still have the other one. So, the decision cannot be made ... we had to leave everything up to the couple."

Eventually, the former employee said, the surrogate mother solved the problem of what to do.

"She said 'I will take the Down baby. I will take the boy. Nobody need to worry’."

She also said the Australian couple knew about both babies, as they were in the same hospital in the same room for four weeks after the birth.

"They definitely knew," she told 7.30.

Family friend says couple expected Gammy to die

After having denied knowing that Gammy even existed, Mr Farnell and his wife now appear to have changed their story.

A family friend has told their local newspaper, the Bunbury Mail, that the parents knew of Gammy and his congenital heart condition, but left him behind in Thailand because doctors said he would not survive.

There is no requirement in Thailand for background checks on parents seeking a surrogate mother.

But neither is there in most Australian states, which only permit unpaid surrogacy arrangements within Australia.

"Victoria requires a criminal check and child safety check to be undertaken," lawyer Stephen Page said.

"It's not mandatory in other places but what is required in other states is you must have judicial oversight.

"At the end of the day, you must have a judge approve the surrogacy arrangement as being in the best interests of the child."

It is illegal for residents of NSW, Queensland and the ACT to pay an overseas surrogate.

For Gammy's sister, it will be up to West Australian child protection authorities to decide whether she stays with her Australian parents.

"If they think there is a risk to this child, they will take action," Mr Page said.

"If they don't think there is a risk to this child, they won't."

Foreign Affairs Minister Julie Bishop has told 7.30 that the revelations "are of course of deep concern".

"The very tragic nature of this case raises a whole raft of issues that must be dealt with at a state and federal level" as well as through working with Thai authorities, she added.

Warning surrogacy industry will move elsewhere if laws change

International surrogacy law expert Jenni Millbank says the case could have a devastating effect on Thailand's surrogacy industry.

"I'm very concerned that this case, which is an exceptional case on many, many levels, is going to be taken as an example to then set in place a series of general rules," she told 7.30.

"And there are certainly many intended parents in Thailand now very concerned [about] whether or not they can bring their children home."

She says a crackdown in Thailand will not stop international surrogacy.

"In recent years we've seen a lot of Australians travel to India, and then more recently to Thailand. If Thailand closes down, people will move on to the next destination," Ms Millbank said.

"And the international surrogacy players - some of them are transnational players - are already setting up in places like Mexico, and elsewhere."

The Department of Foreign Affairs and Trade has updated its travel advice for Australians visiting Thailand in the wake of the surrogacy debate.

DFAT says the legal situation regarding surrogacy arrangements in Thailand is unclear, and Thai authorities are considering new laws to prohibit commercial surrogacy.

The Government is advising parents who are hoping to arrange a surrogate in Thailand to seek legal advice beforehand.