More than 100 gay Australian couples have paid AUS$80,000 (NZ$100,825) to create a baby using rent-a-womb women in the United States, a fertility clinic says.

The controversial scheme, branded as "one-stop baby shopping", is becoming increasingly popular among professional gay men in Sydney and Melbourne, according to Los Angeles-based The Fertility Institutes.

"We've seen more than 125 gay couples from Australia who have gone home with a baby," the clinic's medical director Dr Jeffrey Steinberg told the AAP.

"We're up to six to eight a month now, which is a four-fold increase over two years ago. That makes Australia one of our biggest markets, neck-and-neck with Britain."

The specialist program, the first dedicated to two-father families, allows gay men to pay for surrogate children, a practice which is illegal in Australia.

Couples pick a donor from a list of 400 university students and her eggs are then implanted in a different woman who bears the child. The process allows sex selection and complete anonymity between the male parents and the donor.

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