Sitting cross-legged in pyjamas on the concrete floor of her home, Phalla presses a bottle to a baby girl's lips.

Key points: Surrogacy is illegal in Cambodia but has operated in the shadows

Surrogacy is illegal in Cambodia but has operated in the shadows Cambodian surrogates face up to 20 years in prison for human trafficking

Cambodian surrogates face up to 20 years in prison for human trafficking The intended — or commissioning — parents have remained mostly silent through this ordeal

The baby gurgles, fascinated by Phalla's sparkly blue nail polish.

But Phalla is conflicted about whether the child she is nursing is really hers.

The circumstances are anything but conventional: Phalla was a surrogate paid to carry the baby for a couple in China.

Now, due to stop-gate measures enacted by Cambodian authorities late last year intended to act as a deterrent to the practice of surrogacy, Phalla is among dozens of women forced to raise the child they bore. If she doesn't, she faces up to 20 years in prison for human trafficking.

"Because I was hired to do surrogacy, I feel that the baby does not belong to me — that's not my child," she said.

After police arrested her and "explained" that she was now the baby's mother, Phalla says she eventually came to see it that way too.

"Now when I look at her face, I see my own daughter."

But as surrogates like 35-year-old Phalla are forced to raise a stranger's child, experts are highlighting the sense of loss felt by intended parents, particularly around milestones like Mother's Day.

Surrogates 'accomplices' to trafficking

Surrogates said they underwent fertility procedures at the Central Hospital in Phnom Penh. ( ABC News: Erin Handley )

Commercial surrogacy briefly flourished a few years ago in Cambodia but was outlawed with a snap ban in late 2016, resulting in the arrest of Australian nurse Tammy Davis-Charles and two Khmer associates.

The fraught industry continued underground after an amnesty — which allowed parents from Australia, the US and other countries to collect their babies — expired at the start of 2018.

But in June last year, Phalla, who asked that only her first name be used, was one of 32 women arrested and charged with human trafficking.

Phalla had a caesarean birth in August under police guard. Three months later, she and her newborn were released on bail, on the strict condition that she did not give the child away and promised to raise the child until she turned 18.

Surrogacy is illegal in Cambodia and some surrogate mothers have been charged with child trafficking. ( Cambodia National Police )

Court documents seen by the ABC show that Phalla must present herself — baby in hand — to a local police office once a month. She cannot change her address without the investigating judge's permission, and failing to meet these bail conditions could result in her arrest.

A further 11 surrogates arrested in a November raid were released last month on similar conditions.

No court date has yet been set for the trials, leaving the surrogates in limbo.

Several other surrogates whose names could not be revealed told the ABC they were desperately fearful during their incarceration.

One of the women had to give birth while handcuffed to a hospital bed, while another broke down in tears when thinking about the prospect of years behind bars.

The Cambodian Centre for Human Rights (CCHR) has called for Cambodia to prosecute illegal surrogacy agencies, rather than the women they recruit into "precarious and risky" situations.

"By effectively forcing them to raise a child to avoid prison time, the Cambodian authorities are re-victimising an already vulnerable group," CCHR executive director Chak Sopheap said.

Anti-trafficking official Chou Bun Eng says mothers are determined through giving birth, not genetics. ( ABC News: Liam Cochrane )

But Chou Bun Eng, from the National Committee for Counter Trafficking, has said surrogates are not victims but instead accomplices who "hide" children in the womb in order to smuggle them across borders.

"[They] bring or give the baby to traffickers ... so it seems like they are the ones who join activities with the perpetrators," she said.

When asked about Cambodian women raising children who were not biologically theirs, she said a pregnant woman who gives birth is considered the mother.

Financial pressures driving surrogacy

Phalla is conflicted about whether the child she is nursing is really hers. ( ABC News: Erin Handley )

Phalla already has three children — twin girls, aged eight, and a five-year-old boy.

She learned about surrogacy on the factory floor from a co-worker.

She and other surrogates told the ABC they went to Phnom Penh's Central Hospital to have the embryo inserted into their wombs. But when asked about the practice, hospital staff denied it ever took place.

In late 2017 when Phalla agreed to be a surrogate, garment workers in Cambodia were earning a minimum monthly wage of $US153 ($218).

Dozens of surrogates face up to 20 years in prison for human trafficking. ( Cambodia National Police )

But for carrying someone else's child, surrogates are typically promised $US10,000 ($14,000) — five times more than the yearly salary.

Ros Sopheap, from advocacy group Gender and Development for Cambodia, said putting women in a situation where they were forced to raise a child or go to prison left them with no choice and forced them into motherhood, adding that surrogates were often driven by financial need.

"It's not [just for] themselves alone, but for the families," she said.

"Women always take the burden of the family."

Critics of the transnational surrogacy industry say this perpetuates a power imbalance between men and women from wealthier countries desperate to have a child with their genetic makeup, and the often-impoverished women who carry them.

Miranda Davies, who edited Babies for Sale? — a book about the ethical implications of global commercial surrogacy — said the Cambodian conundrum of surrogate mothers being cornered into raising a stranger's child was unprecedented.

"It's extraordinary," she said. "You don't know how much they've been coerced."

"The bottom line is that this really is about selling babies and exploiting women."

Women's bodies 'fragmented into parts' for industry

Experts say children often have a keen desire to know about their genetic heritage. ( AAP )

Commercial surrogacy is a truly global phenomenon — donor eggs can be sourced in Africa, inserted into the womb of a woman in Asia, and delivered to parents in China or the West.

Israeli couples scrambled to get their babies out of Nepal once the earthquake struck in 2015, while Australians are increasingly travelling to the Ukraine in the hopes of having a child.

According to one chapter in Babies for Sale?: "Women's fertility has served the needs of others since the dawn of history" for political and economic ends.

"But when progressive medical technology is harnessed to treat women as things, servile bodies fragmented into parts and functions, we have to raise questions of ethics and morality."

Surrogacy Australia president Sam Everingham said intended Australian parents sometimes feel unable to properly compensate altruistic surrogates here — who cannot be paid by law — and "they feel they can do more to change the life of a surrogate in a country which allows them to be compensated".

"The Cambodian surrogates released from jail on the proviso they do not give the baby away is certainly a tragic example of forced motherhood, for women who had no intention of raising another child," he said.

The intended — or commissioning — parents have remained mostly silent through this ordeal.

Some couples were unable to conceive because they are gay or have been affected by cancer.

One Chinese father managed to bribe a police guard and see his newborn baby, while his wife remained outside, the BBC reported.

"He held the baby and cried like his heart was broken," his surrogate told the BBC.

Mr Everingham said he felt for the potentially dozens of mothers and fathers who had their baby born in Cambodia but are now unable to raise it.

"The sense of loss around milestones like Mother's Day must sometimes be unbearable," he said.

Nature and nurture in motherhood

This newborn was born under police guard to a Cambodian surrogate and spent his first months in detention. ( ABC News: Erin Handley )

Several surrogates interviewed by the ABC said the moment they saw the baby they birthed, they loved it instantly and wanted to raise it.

Despite there being no genetic link between surrogate mother and child, it's common in many non-Western settings for mothers to feel a sense of connectivity through acts like birthing and feeding, according to Dr Deborah Dempsey, associate professor in sociology at Swinburne University of Technology.

"It may not mean much to a poor woman in Cambodia to be told they are not the mother because they are not genetically related to the child when they are nourishing that child through their body, giving birth and then breastfeeding," she said.

Dr Dempsey added that children often have a keen desire to know about their genetic heritage.

"The research evidence indicates that it is best to tell children about the circumstances of their conception and birth when they are very young rather than wait until they are adults," she said.

Phalla gifted a ring, imprinted with the Khmer character for the letter S, to the baby. ( ABC News: Erin Handley )

In their small village, Phalla and her husband have resolved to tell their now eight-month-old about her origins when the time is right.

"At first I wanted to hide it from her … but I need to tell her before she learns from other neighbours," Phalla said.

In this new parental landscape, she thinks her daughter might have conflicted feelings, too, about whether Phalla is her "real" mother.

"I'm sure she's going to feel that way," Phalla said. "She looks very Chinese, and she may think I am not her parent."