How Successful Is Preimplantation Genetic Diagnosis? What Can Be Done To Make It More Successful?
Highlights From The Conjoint Meeting Of The American Society For Reproductive Medicine And The Canadian Fertility And Andrology Society19 October 2005
Montreal, Quebec- Researchers at the conjoint meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society will present data on the extent of the use of Preimplantation Genetic Diagnosis (PGD) and its effectiveness as treatment accessory to IVF.
PGD, first performed on human embryos in the late 1980?s, requires that one or two cells, or blastomeres, be removed from an embryo and analyzed for genetic or chromosomal defects. PGD is recommended for patients who have a history of heritable genetic disease, unexplained recurrent pregnancy loss or several failed IVF cycles, and for women of advanced maternal age.
Dr Jacques Cohen of Reprogenetics in West Orange, New Jersey will present data from 100 United States IVF centers that referred PGD testing to one reference laboratory. From 1995 to February 2005, a total of 4079 cases testing for aneuploidy (chromosomal abnormalities) were performed by the lab on a total of 33, 572 embryos. The average age of the female patients was 37.5 and 32% of the embryos analyzed were normal. In 3331 of the cases, the patients had embryos transferred; on average, two normal embryos were transferred. For patients in 2540 of these cycles, information was obtained on pregnancy results: there were 931 pregnancies, with 1218 fetal heartbeats observed, 640 deliveries, 341 on-going pregnancies and 164 miscarriages. The researchers observed that the pregnancy rate varied greatly depending on the IVF center and the diagnosis for the patients? infertility.
Jill Fisher of Reprogenetics will report on 539 PGD cases referred to the laboratory from 100 US IVF clinics for testing for translocations. During the period from 1995 to February 2005, the lab analyzed 4,597 embryos to determine if a segment of a chromosome had relocated on that chromosome or moved to another chromosome. The patients? average age was 34 and 19% of the embryos tested normal. However, in 422 cycles patients were able to have an embryo transferred with an average of 1.3 normal embryos per transfer. Pregnancy information was available for 462 cycles; of these, there were 138 pregnancies and 176 fetal heartbeats. There have so far been 113 deliveries among this group, with 40 on-going pregnancies and 15 miscarriages. Previously, these patients had miscarried 88% of their pregnancies; after PGD, the miscarriage rate was down to 9%.
From the Reproductive Genetics Institute in Chicago, IL, Dr. Yury Verlinsky reports on 3631 PGD cycles. Of these, 756 analyzed embryos for single gene disorders and/or preimplantation HLA matching (human lymphocyte antigen) for couples at high risk of having a child with a genetically transmitted disease or who already had a child needing matched stem-cell transplantation from a sibling. This screening resulted in the transfer of 1292 embryos resulting in 244 clinical pregnancies, the birth of 210 babies, and 35 on-going pregnancies. Aneuploidy detection was the goal of 2646 test cycles for poor-prognosis IVF patients with an average age of 38.5. Their testing led to 2110 transfers of 4486 normal embryos, 554 clinical pregnancies, the birth of 411 infants and 91 on-going pregnancies. Couples who were carriers of balanced translocations underwent 232 cycles of PGD with 162 transfers of 275 normal embryos resulting in 57 clinical pregnancies and the birth of 42 healthy children. Overall the accuracy rate for PGD at the Institute was 99.5%; 80% of cases had normal or HLA-matched embryos available for transfer.
Scientists at the Reproductive Genetics Institute also investigated the value of additional testing for aneuploidy for embryos undergoing PGD for Mendelian disorders (genetic diseases) and HLA typing. Two thousand and seventy-four blastomeres were tested for copy numbers of a variety of different chromosomes and the results indicated that without testing the copy number of the chromosome on which the disease causing gene is found, misdiagnosis in PGD for single gene disorders cannot be ruled out. They especially recommend aneuploidy testing for patients seeking PGD for HLA matching because many of those patients are of advanced reproductive age.
Researchers at New York University investigated the connection between embryo aneuploidy and morphology. Reviewing all of their cases of IVF with PGD for aneuploidy done over a three and a half year period, they found that, in 58 cases, 412 of 524 biopsied embryos were aneuploid. Normal embryos were average in appearance and their morphology scores were not significantly different from abnormal embryos. Blastomere asymmetry (difference in the size and shape of blastomeres within one embryo) was seen in 72 embryos, of which 86% tested abnormal. For part of the study, investigators were blinded to all PGD and embryo transfer records and used Day-3 embryo selection criteria (a visual standard) to recommend the likely candidate embryos for transfer. In this exercise, 6 cycles with embryos evaluated solely on looks would have had only aneuploid embryos transferred.
?We need to work to increase the availability of preimplantation genetic diagnosis and its use for patients for whom it is indicated. Strategic use of PGD techniques can ultimately result in fewer pregnancies lost to miscarriage and a reduction in the number of multiple pregnancies when we can be sure we are transferring just one or two normal embryos,? said William Gibbons, MD, President-Elect of SART.