Half of Egg Donors Produce Abnormal Embryos
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Embryos formed from the eggs of young healthy donors show a high level of chromosomal abnormalities, researchers said here today.
Overall, the rate of aneuploidy—an abnormal number of chromosomes—in such embryos was between 40% and 50%, but for some women as many as 83% of the embryos were abnormal, according to reports presented at a joint meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society.
“A significant number of chromosomally abnormal embryos are resulting from the eggs of young reproductive-age females,” said Jeffery Nelson, D.O., of the Huntington Reproductive Center in Pasadena, Calif.
The finding suggests that preimplantation genetic diagnosis (PGD)—which was used in the research to identify aneuploid embryos—should be used more routinely in order to improve the odds of success in assisted reproduction, he said.
Dr. Nelson and colleagues used PGD on 289 embryos from 22 egg donors, all younger than 30. Forty-two percent of the embryos were found to be aneuploid, he said.
However, he said, “the proportion (of abnormal embryos) varied significantly between donors, ranging from 29 to 83%.”
The genetic abnormalities identified by PGD—testing a single cell from an embryo with fluorescent in-situ hybridization (FISH) for extra chromosomes—were not correlated with appearance or rate of growth, the normal ways of judging an embryo. Dr. Nelson said.
A similar result was reported by Paulette Browne, M.D., of Shady Grove Fertility Reproductive Science Center in Rockville, Md. In 275 embryos, PGD showed that 50% were abnormal for at least one chromosome.
In both reports, 64% of the embryo transfers resulted in an ongoing pregnancy, Drs. Browne and Nelson said.
Dr. Browne said that none of the successful transfers in her study ended in miscarriage. “We haven’t necessarily seen higher pregnancy rates, but do see lower miscarriage rates,” she said.
The findings also raise the question of how often such aneuploidy occurs in embryos from young women in general. Dr. Nelson said the discovery may not be generalizable because the process of in vitro fertilization (IVF) itself may cause some of the damage.
On the other hand, he said, it’s “generally believed that about 60% or 70% of pregnancies are lost before a patient clinically realizes she’s pregnant…and maybe that does correlate with the finding that there’s a much higher population of abnormal embryos chromosomally in younger patients than we expected.”
While Drs. Browne and Nelson were reporting on young egg donors, another study—this one of young infertile women—also showed “unexpectedly high” rates of aneuploidy, said Peter Nagy, M.D., Ph.D., of Reproductive Biology Associates in Atlanta.
In a prospective study, Dr. Nagy and colleagues compared 36 infertile women younger than 35 who were having IVF with 62 women older than 35 who were also having IVF, who served as a control group. The average age of the young women was 32.6; the controls averaged 40.8.
Nearly two-thirds of the embryos of the young women (65.8%) were chromosomally abnormal by PGD, Dr. Nagy said, compared with 73.8% for the control group.
The high rates of aneuploidy in all three studies are “rewriting the textbooks,” Dr. Nagy said, adding that conventional wisdom would have put the rate of chromosomal abnormalities in young women between 5% and 15%.
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