Children born after their mother's eggs were matured in a laboratory dish appear to be healthy, according to the first survey of babies born using the technique.
The method, which has been used to create about 250 babies worldwide, is designed to allow normally fertile women whose partners have sperm problems to avoid taking high levels of risky hormone injections before their eggs are retrieved.
Danish researchers told scientists at a European fertility conference Monday that a study of 33 babies born using the technique, known as in vitro maturation, indicates that they are normal, at least up to the age of 2.
"This is still a small study and more children have to be born before we reach any definitive conclusion. However, these results indicate that the IVM method seems to be safe," said the study's leader, Dr. Anne Lis Mikkelsen, a consultant at Herlev University Hospital in Copenhagen, Denmark.
The technique involves removing immature eggs from the woman's ovaries and maturing them in hormones and the mother's blood in a laboratory dish for between 28 and 36 hours. The eggs are then fertilized by direct sperm injection and the resulting embryos are implanted in the womb.
As well as in women who are fertile, the technique is used for women with polycystic ovarian syndrome. Such women often have fertility problems and are at increased risk of ovarian hyperstimulation syndrome, a potentially fatal overreaction by the ovaries to hormone injections given before egg retrieval.
Hormone injections are given to increase the number of eggs that mature in a single menstrual cycle. Without them, normally one egg matures and the rest die. Taking the eggs out before they mature means that with smaller amounts of hormones for given for a shorter period about four eggs can be retrieved while the risks of hormone injections can be avoided.
The chance of pregnancy from transferring one or two embryos is between 18 and 25 percent, slightly lower than for conventional fertility treatment.
Long applied in animals, in vitro maturation was first used on humans in South Korea in 1992. It remains a highly specialized field and only a few clinics worldwide offer the service.
There was a fear that problems such as oversized fetuses might arise, as happened in cattle, said Dr. Johan Smits, a hormone specialist at the Free University of Brussels in Belgium.
"This warrants the clinicians that want to implement the technique in humans to be very careful and to, certainly for the first hundreds of babies, monitor them all to see that there is really no problem of safety," said Smits, who was not connected with the study. "The results here are very encouraging, but other types of studies also need to be conducted."
Roger Gosden, an ovary expert from the Jones Institute for Reproductive Medicine in Norfolk, Virginia, warned that genetic problems seen in animals and suspected in some IVF children could be more likely when the eggs are matured in the lab.
"Because the incidence of those sorts of syndromes is so rare — 1 in 15,000, you need a large series, so studying a few thousand IVM babies is not going to answer the question," Gosden said.
The study involved 33 babies born between July 1998 and January 2000 by in vitro maturation at Mikkelsen's hospital.
One girl was born dead, but her death was thought to be related to the failure of the placenta to operate properly rather than the method of conception. Another girl was born with a soft palate, a common birth defect also not thought to be related to the method.
Birth weights and the rate and type of pregnancy complications and birth defects were normal, Mikkelsen said.
The first 18 children were also examined when they were six months, one and two years old and their parents were questioned about how their children were performing on developmental milestones.
"We found that the development was as we could expect. In about six or seven of the children the language skills were more developed than we would expect, but I think that's due to the parents" and their exceptional motivation, Mikkelsen said.
The findings were presented at the annual meeting of the European Society of Human Reproduction and Embryology.