By Martin Hutchinson
BBC News Online health staff in Madrid
Babies born after their mother's eggs were matured in a laboratory appear to be healthy - despite concerns about the safety of the process.
Egg maturation is a new technique
"In vitro maturation" (IVM) is one of the most recent advances in fertility treatment, and could help women who cannot physically cope with the high doses of powerful drugs needed for normal cycles of IVF to produce large numbers of mature eggs.
Immature eggs are harvested from the ovary and matured in the test tube before being fertilised in the usual way.
However, as with any new treatment, there remained worries that the maturation process could somehow damage the eggs and lead to abnormalities in any resulting babies.
Early results are reassuring - a centre in Herlev in Denmark has so far used IVM to produce 33 babies - 16 girls and 17 boys.
One of the girls was born dead, although doctors said that this was due to an unrelated problem during pregnancy.
Another baby girl had a defect connected to her soft palate, but the remainder were normal at birth, and appear normal two years later.
Better than average
Dr Anne Lis Mikkelson, who led the study, presented at the European Society of Human Reproduction and Embryology annual meeting in Madrid on Monday, said: "The children are aged between two and four years now, and are achieving higher than average scores in their developmental tests - this is probably the result of the exceptional motivation of their parents."
She stressed that the small size of the study meant that the safety of IVM was yet to be completely proven - evidence from thousands of babies born after ICSI, where sperm is injected into the egg, has yet to definitively state whether the procedure is safe, more than a decade after the procedure was introduced.
She said: "More children have to be born by this method before we can reach any definitive conclusion - however, these results indicate that the IVM method seems to be safe."
Fairly few women would be candidates for IVM treatment, as most can tolerate even higher doses of the fertility hormones which doctors use to mature the eggs within the body.
However, some women are judged to be at far higher risk of ovarian hyperstimulation - where an over-response to the hormones places her health in danger.
These include women without fertility problems of their own who are having IVF because of their partner's subfertility, or women with polycystic ovary syndrome.