RANCHO MIRAGE, CALIF. -- Obtaining a preimplantation genetic diagnosis using a 9- or 10-chromosome screening panel would detect 77% of embryos with aneuploidy, preventing their transfer and thereby reducing the miscarriage rate in patients undergoing in vitro fertilization by almost 50%, Dr. Ruth B. Lathi reported at the annual meeting of the Pacific Coast Reproductive Society.
Aneuploidy is the leading cause of first trimester spontaneous abortion, an event associated with substantial financial and personal hardship in patients trying to bear children using in vitro fertilization (IVF).
Dr. Lathi and her associates at Stanford (Calif.) University reviewed cytogenetic testing results of the products of conception in infertility patients who suffered first trimester losses over a 4-year period.
Patients in the program were routinely offered dilation and curettage and cytogenetic testing; the sample included results from all who agreed.
Among 134 karyotypes tested, 59% were abnormal, the vast majority due to autosomal trisomies. Structural rearrangements, monosomy X, triploidy, and tetraploidy also were found.
The most common sites of aneuploidy were chromosomes 15 and 16, although problems on chromosomes 21, 22, and 18 also were frequent.
Investigators compared the detection rates of aneuploidy by panels employed by various national laboratories that specialize in preimplantation genetic diagnosis (PGD) using fluorescent in situ hybridization (FISH). These panels scan for abnormalities on the following chromosomes:
* 5-probe blastomere biopsy: X, Y, 13, 18, 21.
* 5-probe polar body biopsy: 13, 16, 18, 21, 22.
* 9-probe polar blastomere (Reprogenetics): X, Y, 13, 15, 16, 17, 18, 21, 22.
* 10-probe blastomere (Alfigen): X, Y, 8, 9, 13, 15, 16, 18, 21, 22.
The 5-probe blastomere biopsy would have detected about a third of abnormalities and conceivably would have prevented fewer than 20% of the miscarriages in the sample. The 5-probe polar body biopsy did "slightly better," said Dr. Lathi.
The 9- and 10-probe panels yielded a far more accurate, and identical, result, each detecting 61 of 79 (77%) abnormalities. Using these panels to conduct PGD on embryos in the sample could have reduced the miscarriage rate by 46%.
Similar results were seen when the investigators applied their results to subpopulations: only those infertile patients undergoing IVF, or only those with a history of at least two previous miscarriages.
An important caveat with PGD is that it is not 100% accurate when conducted on day 3 embryos, the researchers noted. Some early embryos that appear abnormal may correct themselves, and even the 9- or 10-probe panels missed abnormalities on other chromosomes, although improved molecular detection techniques may refine future panels offered by PGD laboratories.
Dr. Lathi also acknowledged that opting for PGD adds considerable cost--perhaps 20%-30%--to the IVF process. However, "given the medical and emotional costs of a miscarriage, PGD should be considered for [interested] patients," she said.
Authors of the study reported no conflicts of interest concerning financial support used to fund the study.
BY BETSY BATES
Los Angeles Bureau
COPYRIGHT 2004 International Medical News Group
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