The laws on surrogacy vary markedly between different countries - and even within individual countries - in a murky system that can leave children and mothers vulnerable, particularly those in poorer countries.
Here's a look at the situation in some countries.
Germany, Spain, France, the Netherlands
Surrogacy is banned completely, meaning infertile couples are unable to turn to surrogacy as an option. But France does not put a ban on couples bringing in children from surrogacy contracts abroad.
Commercial surrogacy is illegal and can be punishable by law.
It is also illegal for any woman to advertise herself as a surrogate mother.
Couples can only partake in altruistic surrogacy and can consult non-profit organisations during the process.
Once the surrogate mother has given birth to the child, she is the legal carer of her baby until an adoption has been finalised. However, even if she gives the child up initially, she has the legal right to claim it back for two years if she gave one of her eggs in the process.
Surrogacy is banned but there is a flourishing black market, with about 10,000 babies born a year.
Surrogacy is allowed only if the birth mother carries the child for altruistic reasons and does not receive any payment beyond medical costs.
Australian states such as New South Wales forbid people to go abroad and pay a surrogate. Anyone who does so faces two years in jail. But in other states such as Victoria, commercial surrogacy abroad is permitted, though there are no rules or enforceable guidelines.
India, Russia, Ukraine, Georgia
Commercial surrogacy, where the mother is paid, is allowed.
In India, only heterosexual couples can partake in commercial surrogacy. The industry is worth an estimated US$1 billion (S$1.25 billion) a year.
Commercial surrogacy is legal in 19 US states, which have laws recognising compensated surrogacy. Another 10 states allow unpaid surrogacy. Such laws tend to enable would-be parents to change the birth certificate of the child and gain legal recognition of parenthood. All children born via surrogacy in the US are eligible for a US passport, regardless of the citizenship of their parents.
Surrogacy is allowed only when the surrogate mother is a blood relative of the baby's parents. But there has long been lax regulation and oversight.
However, there are proposals to ban commercial surrogacy, and limit such arrangements to heterosexual couples.
Advertisement of surrogacy may also be made illegal, and surrogacy may be undertaken only by parents who had had at least one child.
Source: The Straits Times, London Telegraph, Guardian