Michael Cook, editor of the bioethics newsletter BioEdge and a columnist for Australian Science in the Brisbane Times:

In heterosexual relationships, the birth rate rises when couples are married. One would expect similar dynamics to apply to same-sex couples. For lesbian couples, this is not a huge problem; all they need is a sperm donor. But male couples need surrogate mothers.

Where will these women come from?

Unless the law of supply and demand is repealed, the answer is: where wombs are cheapest. At the moment, this is India, where surrogate motherhood has become a $2.3 billion industry, with the enthusiastic encouragement of some state governments. A recent investigation by the London Sunday Telegraph found there were only 100 surrogacies in Britain last year, but 1000 in India for British clients. The proportion in Australia is likely to be the same.

There are no official statistics, but it appears gay couples account for a substantial chunk of the overseas market. So will the legalisation of same-sex marriage lead to even more surrogate mothers in India? BioEdge, the bioethics newsletter I edit, emailed IVF clinics in India and the US asking whether they were preparing for a rising demand for surrogate mothers.

The answer was a resounding yes.