July 9, 2008

Babies From Frozen Embryos Are Just As Healthy

A new study found frozen embryos are just as healthy as fresh embryos when it comes to weight, risk of birth defects, and premature deliveries.

Danish researchers presented their findings Tuesday during a meeting of the European Society of Human Reproduction and Embryology.

Researchers studied 19,000 babies, and discovered frozen embryos added no risk of birth defect because only the strongest survive the freezing and thawing process.

Dr. Anja Pinborg, a researcher at the Copenhagen University Hospital Rigshospitalet in Denmark said, "We think the reason for the differences is probably positive selection of the embryos for frozen embryo replacement."

To avoid multiple pregnancies, its common practice for doctors to transfer just one embryo into the womb and freeze the rest. The technique reduces the number of times a woman has to undergo a procedure to collect eggs.

Doctors later thaw a frozen embryo and implant it three to five days after ovulation. The process mirrors the way fresh embryos are used. Single embryo transfers are becoming more common but researchers contend there is little information on the results of using frozen embryos.

"Up until now the data has been extremely limited," Pinborg said.  "We wanted to be sure that the procedure had no deleterious effect on the offspring."

Governments and the medical community have been pushing doctors away from transferring multiple eggs at the same time. They claimed it increased the risk of complications.

"If our results continue to be positive, frozen embryo replacement can be accepted as a completely safe procedure, which can be used even more frequently than it is currently," Pinborg said.

In the study, scientists looked at 1,267 children in Denmark who had been born from frozen embryos between 1995 and 2006. They were compared with 17,800 children born from fresh embryos during the same period.

According to data gleaned from Danish national registries, babies in the frozen embryo group weighed about 200 grams more at birth. Researchers said the percentage of pre-term births and low birth weight children was lower.

They found no increased risk of congenital birth defects including conditions such as spina bifida and cleft palate. Fewer frozen embryo babies were admitted to neonatal care units, and pregnancies lasted slightly longer.

"According to this study, which is currently the largest on frozen embryo replacement offspring, these children perform as ... offspring after fresh embryo transplant or even better," the researchers said in their study.

The researchers said the data did not show the freezing process improved a baby's chances. Instead, they explained differences by saying only the strongest embryos survived the freezing process.

Dr Pinborg said the findings are reassuring, "If our results continue to be positive, it can be accepted as a completely safe procedure, which can be used more frequently than it is currently."


On the Net:

European Society of Human Reproduction and Embryology

Copenhagen University Hospital Rigshospitalet