Chromosomal Defects Occur At A High Rate In Embryos Created From Eggs Of Young Donors And Patients Of Young Maternal Age
Highlights From The Conjoint Meeting Of The American Society For Reproductive Medicine And The Canadian Fertility And Andrology Society19 October 2005
Montreal, Quebec- Even embryos formed from the eggs of healthy young donors exhibit a startlingly high number of abnormalities. Researchers presented work today at the conjoint meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society focusing on the use of Preimplantation Genetic Diagnosis (PGD) for embryos created with donor eggs .
PGD is used to increase the chances of pregnancy resulting from an IVF cycle and to prevent the transfer of embryos with identifiable genetic defects. It is recommended for women who have experienced recurrent pregnancy loss, women of advanced maternal age, those who have had previous failed IVF attempts with embryos of good appearance and couples seeking to avoid passing on a heritable disease. Up until now, all information on rates of chromosomal abnormality in embryos has come from infertility patients and those who know they carry a genetic disorder
Hypothesizing that routinely using preimplantation genetic diagnosis for chromosomal abnormalities would improve conception rates in donor egg IVF cases, researchers from the Huntington Reproductive Center in Pasadena, California evaluated 289 embryos from 22 egg donors in 26 fresh and two frozen embryo transfer cycles. They found that 46% of the embryos were chromosomally normal and 42% were abnormal. Only normal embryos were transferred to gestational surrogates on the fifth day after fertilization with an average of 2.4 embryos transferred per cycle. Sixty-four percent of the transfers resulted in an on-going pregnancy. The average age of the donors providing the eggs was 25.8 (all the donors were under 30) but interestingly, the donors? abnormal embryo percentages varied widely from 29% to 83% and it was impossible to tell from the appearance of the embryos which would test normal and which abnormal.
Dr William Kearns and his colleagues at the Shady Grove Fertility Reproductive Science Center in Rockville, MD, sought to determine the incidence of embryonic aneuploidy among the general population. They therefore examined a series of donor egg IVF cases, thus eliminating from consideration the major groups for which PGD is recommended- couples with a history of failed IVF cycles and women of advanced maternal age. They looked at 13 couples who had decided to engage an egg donor due to poor outcomes of their prior therapies. The 13 couples had 14 cycles with a total of 159 embryos examined. The donors? average age was 26.6 (21-31 range). Fifty-two percent of the embryos were found abnormal; 6% could not be diagnosed. All 13 patients had an embryo transfer with clinical pregnancy resulting for eight of the 13 patients. Pregnancy rates among the patients in this group were similar to those in patients using donor eggs who do not use PGD.
At Reproductive Biology Associates in Atlanta, GA, researchers investigated the differing incidence of aneuploidy in young infertility patients as compared with older patients and found that the frequency of chromosomally abnormal embryos is unexpectedly high in those of young reproductive age. In a prospective on-going study, 36 infertile patients (average age 32.5, all under 35), with no prior treatment and representing all diagnoses of infertility proportionally, had IVF with PGD. Their PGD results were compared with a control population of women over 38 (average age 40.7) who were undergoing IVF at the same time. Young patients in the study population had an average of 17.6 eggs retrieved, of which 70% fertilized; the older control patients had 13.5 eggs on average, of which 69% fertilized. The younger women in total had 103 embryos identified as normal and 198 abnormal embryos. The older women had, as expected, a higher proportion of abnormal embryos: 323 abnormal to 116 normal. Of the younger patients, 56% became pregnant, while 33% of the older patients became pregnant.
Eric Surrey, MD, President of SART, remarked, ?PGD may become a very useful technique for maximizing the chances of success of a particular cycle of IVF. And these results do shed light on some of the reasons why a particular young donor or patient might produce many eggs, which fertilize and develop as embryos of normal appearance, but do not result in pregnancy. However, PGD, especially using a single cell, is not fail-safe. Mosaicism, the presence of normal and abnormal cells in the same embryo can confound the results of single-cell PGD.?