A regional Victorian man has pleaded guilty to sexually abusing his infant surrogate twin daughters – and two young nieces from NSW  - in a case certain to fuel debate about international surrogacy laws.

The man was already abusing his nieces when he spent $44,000 to have the twins conceived overseas using a donor egg with the clear intention of sexually exploiting the children. He began abusing them when they were 27 days old and continued for seven months.

The man also produced some of the most depraved exploitation material ever seen, according to the Australian Federal Police. The man was found to have been accessing child pornography for decades.

Surrogacy laws – including the legal aspects of international surrogacy – are already being examined by a federal parliamentary committee.

The 49-year-old, who cannot be named, will become only the second person in Australian history convicted of the federal offence of child trafficking, it is understood.

On Thursday, he pleaded guilty to 37 charges, including the production of almost 17,000 images and videos of child abuse, and upskirt material taken of women on V/Line trains, between 2009 and 2014.

Almost 300 images and videos featured the twin girls, who were born in Asia in March, 2014, using a donor egg from the Ukraine.

The twins' country of birth is suppressed, but the centre the man and his wife used boasts that they have helped dozens of Australian couples have children.

The man's wife first suggested surrogacy in 2012 after the couple of 26 years had failed with natural conception and IVF, and were unable to adopt.

Federal prosecutor Krista Breckweg said the man asked his wife to have an abortion in the early 90s when she fell pregnant, and appeared to not be interested in parenthood until after he started abusing his nieces in 2009.

The man, who was known on various child abuse forums by the name Candy, had told other members about the impending surrogate births and his intention to abuse the girls.

He also suggested to his wife that one of the twins should be named Candy.

Ms Breckweg made an application for Judge Susan Cohen to view a selection of the material before sentencing the man. "Your honour, seeing is believing," she said.

"Seeing and listening provides a more realistic example of the depravity and the harm caused by this offending."

The twins – who are now in the care of the Department of Health and Human Services – were abused while the man was feeding, bathing and changing them. The man's wife was in no way aware or complicit in the offending, according to the AFP.

On 57 occasions, the man produced images or films which showed writing in felt marker on the twins, which, in some cases, gave the man entry into other online child abuse networks. The twins were abused for seven months.

The man first came to the attention of police when an image of an unidentified victim was sent to the AFP in November 2014.

The victim was found to be one of the man's nieces. The sisters had been abused from the ages of four and six, after the man rekindled a relationship with his estranged brother in NSW.

He often bought his nieces gifts and took them to Sydney's Royal Easter Show, and repeatedly requested that they stay with him in Victoria.

The man boasted on online forums ahead of their expected visits, and encouraged those who posted comments on his images. He also shared information about how he had drugged the girls prior to his offending, and subsequent images appeared to show them sleeping.

The man's regional Victorian property was raided on November 26, and computers, cameras, hard drives and mobile phones were seized. Among the items seized was also a modified gym bag, which the man used, along with his mobile phone, to make five films under the skirts and dresses of women on V/Line trains in October, 2014.

He made full admissions to police about the offences, and said he had been interested in child abuse material since the 1990s, but had repeatedly tried to resist his urges by deleting the material, most recently in 2007.

He sat in silence staring into the middle distance in court, his hands clasped in front of him. There were no supporters of the man in court, but several friends of his wife, from who he is now estranged.

In December last year, Attorney-General George Brandis asked the standing committee on social policy and legal affairs to examine domestic and international surrogacy. The committee is due to report by June 30.

International surrogacy was last brought into question with the baby Gammy case in 2014, which resulted in a twin with Down syndrome being abandoned in Thailand.