Thousands of couples are travelling to clinics in the US where they can choose the sex of their next child. Dr Jeffrey Steinberg, the leading figure in American commercial sex selection, says that half of his clients come from countries where the controversial procedure is banned, such as Australia, Germany, Britain and Canada. In the United States we really guard and cherish reproductive choice and we are very reticent to allow the government to impinge on that," says Steinberg. Over the past three years he has treated 2,000 couples.

Most couples tell Steinberg that they have come to him to balance their family. "Usually these couples have four or five children of one sex and desperately want one of the opposite sex," he says. Americans and Canadians have a preference for girls; Indians and Chinese for boys; and Latin Americans are evenly split. He denies that his work represents a step towards "designer babies".