Reprogenetics, West Orange, NJ, USA
Email: munne{at}embryos.net
Dear Sir,
The efficiency and reliability of preimplantation genetic diagnosis (PGD) for aneuploidy is closely linked to the stage at which eggs or embryos are biopsied, the finesse with which the procedures are applied, the number of cells removed with respect to developmental stage, and the number of chromosomes assessed. Not only do the actual PGD procedure and the selected patient population play roles in the final success of the PGD test, but the impact of biopsy may adversely affect outcome dependent on the general circumstances in which a given IVF laboratory operates. In other words, biopsy of the cleaved embryo may in some instances alter the survival negatively even if only one cell is removed. It is dependent on conditions of manipulationwhich vary widely from laboratory to laboratoryand embryo culturewhich varies even more!but it certainly is affected disproportionately when more than one cell is removed.
Reports arguing the success of PGD often lack a greater comprehension of patient and laboratory differences and candour when describing the whole picture; they fail to consider the intricate balance between patient care, application of technology and clinic-related differences. It is in this context that we would like to comment on the study of Staessen et al. (2004). This study describes the effect of PGD by biopsying two cells, instead of one, from cleaved embryos. The fact that the outcome was rather disappointing is not surprising since it was already shown in two previous reports that removing two cells from cleaved embryos on day 3 can be akin to harming the embryo beyond repair (Bahçe, 2003
; Magli et al., 2004
). In spite of what the authors assert, it is not the rate of unaltered blastocyst development that occurs as a result of the removal of one or two cells that is important. Rather, it is the fact that the portion of cells in the inner cell mass is diminished when biomass is removed from early embryos proportionately. We strongly suggest that the group in Brussels revisits this important discussion, since their presentation is, at best, confusing. In applying such an invasive procedure as biopsy in a laboratory that only has an implantation rate of 11% when blastocysts are replaced, it is not surprising that the biopsyregardless of number of cells removedharms the embryo's further development. Fortunately, the strength of PGD's selection process compensates for this procedure's related detriment in the Staessen study, strengthening, and not weakening, as the author's contend, the ability of chromosome analysis to compensate for the already artificially induced injury. In years to come, this report will probably be hailed by opponents of PGD for infertility. Let it be said here that this study, in spite of its good intentions, particularly with its use of randomization, does not prove that aneuploidy testing in cleaved embryos, using a restrictive number of probes for chromosomes, does not work. On the contrary, it shows that the test is helpful, even when conditions are suboptimal.
References
Bahçe M (2003) Effect of different biopsy procedures on implantation rates. Proceeding of the Fifth International Symposium on PGD. Antalya, Turkey, 57 June 2003. O-23.
Magli MC, Gianaroli L, Ferraretti AP, Toschi M, Esposito F and Fasolino MC (2004) The combination of polar body and embryo biopsy does not affect embryo viability. Hum Reprod 19, 11631169.
Staessen C, Platteau P, Van Assche E, Michiels A, Tournaye H, Camus M, Devroey P, Liebaers I and Van Steirteghem A (2004) Comparison of blastocyst transfer with or without preimplantation genetic diagnosis for aneuploidy screening in couples with advanced maternal age: a prospective randomized controlled trial. Hum Reprod 19, 28492858.