Modern couples seeking similar guidance are not short of advice. Women desiring sons need to eat a high-sodium, high-meat diet. They should make love standing up and try to achieve orgasm.

Eating lots of calcium and desserts should help to conceive a daughter, as will adopting the missionary position when making love (avoiding orgasm this time). Male partners should take plenty of hot baths before intercourse.

But particularly keen couples need no longer rely on such unproven methods. Ultrasound scanning, sperm sorting, pre-implantation genetic diagnosis and testing foetal DNA in maternal blood can all make the wish for a particular gender a reality, albeit with varying success rates.

Sex selection raises a host of ethical issues, for which there is little hope of consensus. Those opposed to it cite the impact on gender equality, psychological harm to the child from living up to gender stereotypes and the slippery slope to eugenic practices as reasons to avoid the technology. More-over, they claim that there is no room for sex selection in parent-child relationships based on unconditional love.

Those in favour claim instead that couples should have the liberty to decide for themselves whether sex selection is appropriate, so long as that choice does not cause harm to others.

Little is known about what happens to the children born from these procedures, largely because they are so new. Critics’ predictions of gender imbalance have been answered in Australia, where sex selection was practised in New South Wales until banned by a national ethics committee last year.

At one clinic where the procedure was offered, nearly two thirds of couples selected a girl. And a US study published earlier this year showed an equal preference for boys and girls among 229 women undergoing in-vitro fertilisation.

Developing world statistics paint a very different picture. In India cheap ultrasound machines are readily available, enabling what some experts have termed a “gendercide”. The ratio of girls to boys has fallen steadily for more than 20 years, particularly in rural areas. The latest census is alarming: in Dibang Valley there are only 788 girls for every 1,000 boys; the normal ratio is 950:1,000.

A similarly worrying ratio exists in China, which again is more prevalent in rural areas where sons are desired by farming families. Despite the relaxation of the one-child policy, there are now only about 833 girls for every 1,000 boys.

Ainsley Newson, a researcher in medical ethics at Imperial College London, is a British Association Media Fellow at The Times.

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