Increasing numbers of young women are freezing their eggs to pursue their careers as the pioneering process becomes increasingly successful, according to a new report.

New research shows the egg-freezing technique that allows a woman to stop her biological clock for 10 years or more has greatly improved. The procedure used is similar to in-vitro fertilisation (IVF). Drugs stimulate egg production and these are retrieved from ovaries and frozen.

When the woman is ready to use them the eggs are thawed and fertilised in a laboratory. The embryos are implanted in the uterus and, if all goes well, a normal pregnancy follows.

To get an overview of success rates a research team led by Dr Kutluk Oktay, of the Centre for Reproductive Medicine and Infertility in New York, contacted every centre in the world that reported results of egg-freezing using conventional methods between January 1997 and June 2005.

After all but one returned data, the team found the overall live birth rate for each embryo successfully created using a thawed egg and placed in a woman's uterus was 22%. This increased to 32% between 2002 and 2004. Compared with fresh eggs, with which live birth rates in the US average 43% for women under 35, that might not sound great, but ideally a woman would have multiple eggs on ice to compensate for lower efficiency of thawed eggs.

However, a second analysis from Dr Oktay's group dealt with a newer technique called vitrification, in which eggs are frozen so quickly ice crystals can't form, which was even more promising. "The fast-freezing technique appears to have caught up with fresh eggs," said Dr Oktay, whose results were presented at a meeting of the American Society for Reproductive Medicine in New Orleans.

He said, however, that so far only 60 babies have been born using this technique, and with such low numbers it isn't possible to be certain of success rates. Dr Oktay and other fertility specialists believe the efficiency of egg-freezing technology will improve further.

One company, Extend Fertility, based in Woburn, Massachusetts, markets "insurance" egg-freezing to professional women, and recently announced seven babies have been born during the past 12 months.

No public records exist of the numbers of women who have used insurance freezing, but fertility specialists estimate it's in the thousands worldwide, reports New Scientist.

Professor Richard Fleming is scientific director of the Glasgow Centre for Reproductive Medicine (GCRM), which has offered women the chance to freeze their eggs and preserve their fertility since November.

He said: "For a long time now we have been able to freeze embryos so that couples themselves could make a decision on when to have their pregnancies.

"What is new is that the technology now means a woman doesn't need a partner to put her fertility on ice. She can make the decision herself. There are a number of private centres in England that offer this service and maybe some other clinics in Scotland will do it now the technology is more reliable."

Professor Fleming said the number of women using the service in Scotland, which costs about £3100, was still in single figures. However, he said at least 100 women had used it at one clinic in Birmingham over the past four years.