A gay Singaporean doctor's failed bid to adopt his American-born biological son is the first application by a single to adopt his own child conceived through surrogacy here, the Ministry of Social and Family Development (MSF) told The Sunday Times.

The man travelled to the US and paid US$200,000 (S$267,000) to father a boy through surrogacy arrangements. Going by judgement grounds released on Tuesday, a district judge rejected his bid to adopt the child - now four years old - whom he brought back with him to Singapore.

While there are no surrogacy services allowed here, one centre in the United States said it has seen a doubling of inquiries from Singapore each year over the past two years, with more heterosexual couples turning to surrogacy as the stigma of infertility has lessened, the centre said.

The British Surrogacy Centre of California handled 18 clients from Singapore and received more than 100 calls and e-mails from prospective Singaporean parents over the past year, chief executive Barrie Drewitt-Barlow told The Sunday Times.

Of the inquiries, about half were from heterosexual couples, while 30 per cent were from gay couples and 20 per cent single men.

While most of the five to eight Singaporean couples the centre used to see a year were gay men, its clientele now includes more heterosexual couples, said Mr Drewitt-Barlow.

"The gay men need surrogacy because they have no (other) option as they cannot carry babies themselves, (while) a straight couple uses surrogacy because they have a medical problem and, for years, the stigma that went with infertility was something a lot of women... couldn't admit to or deal with. This is not the same any more," he said.

Heterosexual couples go to the US as they can be established as the legal parents before the baby is born.

Through the Californian courts, the centre can apply to establish its clients as the legal parents on a birth certificate, rather than the surrogate mother.

At least 15 children born this year were brought back to Singapore and passed off as children born to the couples overseas, and not a surrogate, said Mr Drewitt-Barlow.

The entire process, including surrogacy and legal fees, costs about US$130,000 to US$150,000.

Surrogates are screened and assigned their own manager and social worker, and make about US$30,000 to US$50,000, said Mr Drewitt-Barlow.

Another US-based agency, Circle Surrogacy, has seen a consistently steady number of Singaporean clients since 2008. It serves fewer than five such clients a year.

In general, its surrogate mothers come from across the US and range from those in their early 20s to late 30s. They might also have families of their own.

The agency added that it matches surrogate mothers to the client through screenings, questionnaires and even psychological testing.

Singapore's Ministry of Health has guidelines that prohibit assisted reproduction centres from carrying out surrogate arrangements.

Other countries such as India, Thailand and Cambodia have also cracked down on surrogacy, especially following the case of "Baby Gammy" in 2014, when a boy with Down syndrome was born to an Australian couple through a Thai surrogate mother and allegedly abandoned. A judge later ruled that the child was not abandoned.

In the recent gay Singaporean doctor's case, District Judge Shobha Nair said: "The very idea of a biological father seeking to adopt a child after paying a surrogate mother a sum of US$200,000 to carry his child to term reflects the very thing the Adoption Act seeks to prevent - the use of money to encourage the movement of life from one hand to another."

The MSF's director of social welfare, as the court-appointed Guardian-in-Adoption, investigates an average of 360 adoption applications per year, the ministry said. It declined to provide the proportion of applications that involve children conceived through surrogacy.

Applications by singles form less than 5 per cent of adoption applications investigated, an MSF spokesman added.

Family lawyer Rajan Chettiar said that he has received inquiries about surrogacy, but these are fewer than 10 a year. "A major issue is that surrogacy is transactional. Payment is involved. That is not really a relationship that society here will want to support."

The main challenge after the child is born, said Mr Chettiar, is when parents want to adopt the surrogate child in Singapore, as in the doctor's case.

"Even if it's a married couple, trying to adopt the child will fail simply because the child was born through surrogacy," he said. "From a personal, emotional standpoint, I understand this man's issue, but the law still stands."

One of the doctor's lawyers, Mr Ivan Cheong, agreed. He said: "It would appear that if a child is born through surrogacy, an adoption application would not succeed regardless of the sexuality of the adopting party or parties (for a straight married couple)".

He said that he has seen about four such cases before.

"A primary challenge is the removal of the stigma of illegitimacy in relation to the child who would not be deemed to be born out of lawful wedlock and also to transfer the parental rights to that of the adoptive parents away from the (presumed biological parents of the child)," said Mr Cheong.

"Citizenship is entirely at the Immigration and Checkpoints Authority's discretion, although adoption may help. The bar right now really is the issue of surrogacy," he explained.

•Additional reporting by Rachel Au-Yong