Sperm sorting technique

A team of US scientists from the Genetics and IVF Institute in Fairfax, Virginia reported to the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) last week that they had devised a method of sorting sperm by gender. The technique, called MicroSort, can greatly improve the number of female embryos created in IVF and is said to be accurate in 90 per cent of cases, allowing prospective parents to have a say in what sex their child will be.

Those using PGD (pre-implantation genetic diagnosis) in order to avoid their children inheriting an X-linked disease - such as haemophilia or muscular dystrophy - will be able to use this technique to increase the chance that embryos selected for biopsy are female. A female child might be a carrier but would only be affected by an X-linked disease if two copies of the gene for the disease are inherited. Boys with one copy of the gene will be affected by the disease.

The sperm sorting technique relies on the fact that the X chromosome carries more DNA than the Y chromosome, and is therefore 'heavier'. In a 'modified flow cytometer instrument', most of the 'heavier' sperm separates from the 'lighter' sperm, after being dyed with a fluorescent marker and fired at high speed under a laser. The laser sorts the sperm according to the amount of fluorescent marker it has identified. Dr Harvey Stern said that although the technique is still in the trial stage, the team know that it 'substantially increases the chance of a couple having a child of a particular gender'. He reported that 297 pregnancies had been achieved using the technique, and that 187 babies had been born so far.