What are the trade-offs between one-cell and two-cell biopsies of preimplantation embryos?

The fast changing landscape of reproductive technologies has experienced its share of controversies, among which is the genetic screening of preimplantation embryos. In principle, preimplantation genetic diagnosis (PGD), for known genetic afflictions, and preimplantation genetic screening (PGS), for aneuploidy detection, provide an option for fertile and infertile patients to detect any abnormal embryos and thus presumably augment implantation and take-home baby rates. In practice, PGD and PGS are not yet offered by all fertility centers with only 4–6% of IVF cycles combined with PGD in the USA (Baruch et al., 2007). Nonetheless, PGD is one of the fastest growing technologies in assisted reproduction (Sermon et al., 2007). Some experts even predict it to become one day a procedure ancillary to routine IVF cycles. Yet a divide characterizes the field, notably with respect to the potential clinical benefits of PGD/PGS. Regardless of which side of the divide a clinic may stand on, everyone agrees that intensive efforts should be placed on elucidating the true value of PGD/PGS. Only then will practitioners and patients be in a comfortable position to offer, select, or opt out of its use for treatment. While many facets of PGD remain investigational in nature, the technology already entered the clinical arena with even an aggressive use of it by some centers. It is striking that despite the hundreds of IVF laboratories performing PGD/PGS worldwide and the 50 centers reporting to the ESHRE PGD Consortium (Sermon et al., 2007), the scientific literature appears somewhat dominated by a handful of groups. Together, these investigators have made significant strides. Nonetheless, a call must go out to others towards a more concerted involvement and scientific advancement of PGD. PGD/PGS is a complex procedure that includes a plethora of technological hurdles, from the biopsy to the processing of extracted blastomeres and the final diagnostic analysis. PGD can be used to detect an ever-increasing number of diseases, over a 100 different genetic conditions to date (Baruch et al., 2005). Ongoing efforts have also focused on the diagnostic procedures, with the testing of alternative and/ or complementary approaches. FISH and PCR are widely employed with comparative genomic hybridization and spectral karyotyping representing some of the newer ones on the docket (Wells, 2004; Donoso et al., 2007). But grossly understudied is the methodology used for cell removal along with all of the critical laboratory procedures surrounding the biopsy itself. In this vein, experts have identified a number of pivotal discrepancies in the PGD lab procedure, among which are the cell removal technique, the fixation protocol, the selected set of chromosomal probes for FISH and the number of cells used for biopsy (De Vos and Van Steirteghem, 2001; Cohen and Munné, 2005; Cohen et al., 2007; Munné et al., 2007). The study published in this issue by Goossens et al. precisely addresses one of these long-standing questions as to whether more good than harm ensues from the biopsy of two cells versus one cell. This study is incredibly timely, especially in light of the most recently published article by