Preimplantation Genetic Diagnosis
This year marked the 60th anniversary of the American Society for Reproductive Medicine (ASRM). The annual meeting, held in Philadelphia October 16-20, was given the subtitle "60 Years in Progress." The conference is clinically oriented, but a significant proportion of the sessions this year were dedicated to the latest improvements in laboratory/ embryology technology. Our goal in infertility treatment is to design safe stimulation protocols and to limit the number of embryos transferred in order to avoid multiple gestations. Obviously, high pregnancy rates need to be maintained as well. A number of presentations were dedicated to these issues.
Most chromosomally abnormal embryos fail to implant. In addition, the majority of the early pregnancy losses are due to chromosomal abnormalities. Preimplantation genetic diagnosis (PGD) of embryos obtained after in vitro fertilization (IVF) has revealed an abnormality rate as high as 80%. Although rates are higher among older women, they may be as high as 30% among women 30 years of age. PGD can identify the genetically abnormal embryos, and selection of the healthy embryos could improve implantation and pregnancy rates. In addition to numeric and structural chromosomal abnormalities, PGD also enables us to screen for certain gene defects. PGD is thus recommended for women with recurrent pregnancy loss, women who are at advanced reproductive age , and for couples with known genetic abnormalities.
Colls and colleagues evaluated PGD for women with recurrent pregnancy loss (defined as 3 or more previous losses). The control group consisted of women with 0 or 1 previous loss who also underwent PGD. Fluorescent in situ hybridization (FISH) was performed on a single blastomere biopsied on Day 3; 9 chromosomes were assessed. Pregnancy and loss rates were evaluated in 3 age groups and were found to be comparable between the recurrent loss and control groups. During the PGD cycles, the average loss rate was 13% in the recurrent loss group. This compared favorably to the 88% loss rate in previous pregnancies in the same group.
Werlin and colleagues compared IVF outcome with or without PGD among patients with recurrent loss or advanced maternal age. Assignment to the PGD or control group was randomized. Two thirds of the biopsied embryos had an abnormal karyotype. The rate was similar in the recurrent loss and advanced maternal age groups. There was a trend for higher pregnancy rates in the recurrent loss (60% vs 41.7%) and advanced age (40% vs 23%) groups with PGD when compared with controls within the groups.
Turkaspa and colleagues evaluated IVF outcome in a cohort of patients undergoing PGD (inclusion criteria: age > 35 years, recurrent loss, previous failed implantation) and compared implantation (IR) and pregnancy rates (PR) to IR and PR in previous non-PGD cycles of the same women. Genetic analysis was performed on the first and second polar bodies and on a single blastomere obtained on Day 3. In the PGD cycles, 35% of the embryos implanted, resulting in a 68.5% take-home-baby rate. Spontaneous abortions occurred in 26.9% of the cycles. In the PGD cycles, IR was up from 7.2% (non-PGD control cycles), spontaneous abortion rates were down from 68%, and the take-home-baby rate improved from 32% to 68.5%. Stevens and colleagues, on the other hand, failed to demonstrate a benefit with PGD in a randomized study of women older than 35 years. Ongoing pregnancy rates were similar (72% in the control group and 52% in the PGD group)
Selection of the genetically healthy embryos for transfer may enable a reduced number of embryos to be transferred without compromising pregnancy rates. This should result in fewer multiple gestations. Oter and colleagues compared IR and PR in a group of women > 35 years undergoing IVF who either did or did not undergo PGD. Significantly fewer embryos were transferred in the PGD cycles (1.5 vs 3.7 embryos). Pregnancy rates were comparable (33% vs 30%). Implantation rates were significantly higher in the PGD group (24% vs 12%, P < .001). This study showed that PGD may be able to help us identify the embryos that are more likely to implant, thereby reducing the number of embryos that would need to be transferred and thus the number of multiple, especially high-order multiple, gestations.
Medscape Ob/Gyn. 2004;9(2) © 2004 Medscape
Cite this: Highlights From the American Society for Reproductive Medicine 60th Annual Meeting - Medscape - Nov 08, 2004.