Claims have been made that a new technique, available in the UK, is being used in other countries to select the sex of embryos for social reasons. According to a report published in the Mail on Sunday, blastocyst transfer results in more male embryos than female being transferred to the womb during IVF treatment.

The technique, which involves the transfer of an embryo five or six days after fertilisation, as opposed to two, is already used because it allows clinicians to choose the healthiest embryos. But Spanish scientists have shown that the technique produces more boys because at that age the male embryos generally appear healthier than the females. Research showed that if an embryo was transferred after six days, there was a 65 per cent likelihood that the baby would be a boy. At two days, there is a 50:50 chance of it being a boy or a girl.

Concerns have been expressed that the technique will be used to introduce sex selection for non-medical reasons in this country. Nuala Scarisbrick, representing the charity Life, said that 'there are some people who only want boys and, therefore, some people will offer this procedure to create boys in this country'.

But it has been pointed out that the procedure would not guarantee a child of a particular sex, and neither would it guarantee a baby at all, as not all embryos would survive until the later stage. Keeping an embryo in a laboratory might also cause it to develop abnormally, Dr Dave Morroll of Nurture was reported as saying. The Human Fertilisation and Embryology Authority said that blastocyst transfer for non-medical sex selection would not be allowed in the UK.