Pattharamon Janbua claims the biological father of the twins came to a Bangkok hospital after she gave birth six months ago and saw both children - the girl, whom he took home, and her brother, called Gammy, who has Down sydrome and is critically ill.

But the West Australian parents have denied abandoning Gammy. The ABC quoted the unidentified father as saying a Thai surrogacy clinic doctor only told him and his wife about the girl.

The man was quoted as saying he had a lot of trouble with the surrogacy agency and had been told it no longer existed.

Gammy has stayed in Ms Pattharamon's care in an impoverished village in Thailand. He is receiving treatment in hospital for a lung infection.

When told of the father's comments, Ms Pattharamon lashed out at him, saying she had forgiven the Australian couple but had now changed her mind and might sue them.

“I am very upset that the father said like that. I really want him to come to Thailand to see me … I would like to talk with him in front of the media,” she said.

“No one can lie and the truth will come in the public … people who don’t know me will think that I’m a bad person."

Earlier, she told Fairfax Media  and Thai television that the father had come to the hospital and seen the twins.

The father, who was in his 50s, “came to the hospital to take care of the girl but never looked Gammy in the face or carried him”.

“He did not buy milk for Gammy. He only bought milk for the girl,” Ms Pattharamon said from a Thai hospital where Gammy is receiving treatment.

“The twins stayed next to each other but the father never looked at Gammy … not one bottle of milk did he give Gammy,” she said.

“I could say he never touched Gammy at all.”

The Thai doctor who monitored Ms Pattharamon during her pregnancy and delivered the babies told Fairfax Media he does not know whether the Australian parents came to the hospital where the twins were together after the birth.

Dr Kasemsit Keawkeattikun, family planning department from Bangkok's Vajira Hospital who presided over the births said confirmed the girl was also unwell and and was kept in the hospital for about a month before she was taken to Australia.

"I couldn't remember that Australian father came to the hospital because many people came to the newborn room and they not identify themselves to me, he said. "After the baby born it was not my responsibility. I passed  to the newborn department."

The Thai surrogate mother has said in a number of interviews she loves Gammy and wants to keep him.

But the couple’s claim raises new questions about his future as a fund-raising campaign to pay for life-saving surgery for a congenital heart disease, treatment for a lung infection and his long-term care topped $210,000.

Stephan Page, one of Australia’s leading surrogacy lawyers, said that, under Thai law, Ms Pattharamon was Gammy’s legal mother “so it would require her agreement for the baby to go back to the parents”.

Thai authorities are cracking down on surrogacy in Thailand, declaring that any baby born under surrogacy arrangements would need the permission of the Ministry of Foreign Affairs to take the baby out of the country.

Fairfax Media has been unable to contact the surrogacy agent who operated out of a house in Bangkok.

Ms Pattharamon said she met the agency’s American owner when it was discovered she was having twins.

Ms Pattharamon said Gammy is responding better to a lung infection after being transferred to an international-standard hospital in Thailand’s Chonburi province.

Ms Pattharamon wept when told by a representative of Australian charity Hands Across the Water she will have enough money to care for Gammy.

“My children love Gammy very much and want him to come home,” she said, referring to her two other children, aged three and six.

Following the crackdown on surrogacy clinics, dozens of Thai clinics have pulled down or changed websites advertising surrogacy and gender selection IVF procedures that were popular with Australians.

The crackdown has left about 200 Australian couples who have surrogacy arrangements in Thailand facing an uncertain future for their babies.

Many had taken on trust the advice of Thai doctors and surrogacy agents that the agreements they signed were a reliable pathway to parenthood.

The deputy director of Thailand’s Department of Health Services Support, Tanes Krassanairawiwong, said Gammy’s case was raised at a meeting of medical and legal officials last week that discussed planned changes to IVF regulations.

“I used Gammy’s case as the example of a negative effect from not using a blood relative as the surrogate mother,” Mr Tanes said.

“[Blood relatives] would not leave behind a child like that,” he said.

“Even though it is not illegal, since there is no law to control it, morally this is very wrong.”

Officials threw Thailand’s surrogacy business into crisis after the meeting when they declared that altruistic surrogacy would be allowed only where a married couple could not conceive a child and engaged a blood relative to carry their child.

Any arrangement where money is provided to the surrogate to carry the child was illegal, they said.

And any foreigner removing a child from their mother to another country permanently without permission from Thailand’s Ministry of Foreign Affairs would face prosecution under human trafficking laws.

Demand for in vitro fertilisation, with the option of choosing the child’s gender, has been growing at more than 20 per cent in Thailand where the industry has been largely unregulated.

The country has 44 IVF clinics with four new facilities opening last year.

Draft legislation proposing the banning of commercial surrogacy and the brokering of surrogacy arrangements through third parties had sat dormant in Thailand’s parliament for four years, despite reports that some unregistered surrogacy operators had been exploiting vulnerable surrogates and intending partners.

But the military junta that seized power on May 22 has swung its support behind the Medical Council of Thailand, the organisation in charge of enforcing medical ethical standards in Thailand, which has been steadily tightening guidelines on IVF and gestational surrogacy.

After reports in mid-July that Chinese were flooding Bangkok clinics for IVF procedures to select a baby’s sex, authorities raided more than a dozen clinics.

Confidential documents on at least one Australian couple awaiting the birth of twins to a Thai surrogate woman were seized, leaving them unable to check on the condition of their babies.

Authorities have warned that clinics advertising gender selection would be prosecuted.