Published online 26 January 2009 | Nature | doi:10.1038/news.2009.58
Corrected online: 28 January 2009

News

First IVF pregnancy after rapid egg screening

Colourful procedure finds missing or extra DNA.

Human egg and pipetteA new technique analyses DNA jettisoned by the egg for chromosomal abnormalities.CARE Fertility Group

A 41-old-woman is the first to become pregnant after undergoing a speedy new technique to screen her eggs. The procedure identifies the eggs most likely to develop into viable embryos so quickly that embryos do not need to be frozen before they are used for in vitro fertilization (IVF).

IVF, in which eggs are fertilized in a dish and the resulting embryos transplanted into the womb, has a low success rate. Just 24% of IVF attempts with fresh eggs result in a live birth, and the odds shorten with age. Many women have the fertilized embryos frozen for use in future treatment cycles, but just 17% of those frozen embryos lead to live births.

Most IVF failures are attributed to genetic abnormalities in the egg — up to half of eggs in younger women, and up to 75% in women approaching 40, have missing or extra chromosomes.

The new technique, called array comparative genomic hybridization, shows up chromosome losses or gains, allowing doctors to select only embryos that came from eggs with the normal 23 pairs of chromosomes for future use.

"It lets you keep the embryos worth freezing and using, and screen out those with no real future, so it makes the whole process more efficient," says Tony Rutherford, chairman of the British Fertility Society.

A woman who had undergone the procedure at the CARE Fertility Centre in Nottingham, UK, is now in her second trimester, after 13 cycles of unsuccessful IVF. Eight of the woman's eggs were tested, of which two contained the right number of chromosomes. The two embryos derived from those eggs were then transferred into the woman's womb.

"Interestingly, perhaps demonstrating the potential for this technology, these embryos were not the best looking down the microscope," says Simon Fishel, managing director of CARE Fertility. They may not have been chosen for transfer without the new technique, he explains. The baby is due this spring.

Seeing spots

The new method uses DNA taken from the polar body, a chromosome-containing 'sack' that is normally jettisoned from the egg later in development. While the egg is being fertilized and cultured, the DNA extracted from the polar body is labelled with a fluorescent chemical and hybridized with thousands of probes printed on a glass slide. If DNA is missing, a red spot appears. Too much, and there's a green spot. But if all is normal, the slide breaks out in yellow dots.

ADVERTISEMENT

The technique delivers results in 1–2 days, a significant advance over its more basic predecessor, called simply comparative genomic hybridization, which took 5 days to analyse. But doctors hope that it will deliver similar success rates. In 2007, the team from CARE Nottingham announced that the technique doubles the chances of a woman having a baby through IVF.

At present, women undergoing IVF may have two or more embryos re-implanted to maximize their chances of success, but this also raises the chances of multiple births. The new technique may mean that, in future, women can have just one embryo implanted without reducing their chances of pregnancy.

"Although it is still at a very early stage, this technique may offer a new diagnostic and therapeutic hope to couples who suffer from repeated implantation failure in IVF," says gynaecologist Stuart Lavery, who is director of IVF at London's Hammersmith Hospital. 

Corrected:

We incorrectly stated in an older version of this article that array comparative genomic hybridization boosts the success rate of IVF. The article has since been corrected.
Commenting is now closed.