Preimplantation genetic screening is alive and very well: Really?

12 09 2013

To the Editor:

The September issue featured Views and Reviews on preimplantation genetic screening (PGS), including an editorial by Meldrum (1), declaring PGS “alive and very well,” four reviews of technical aspects of the procedure, and three articles by the Scott group. Unfortunately, lacking was a critical and balanced presentation of the subject.

The concept of PGS is not new. It was proven useless in a prior incarnation, though unfortunately only after thousands of women reduced pregnancy chances by utilizing the procedure (2). Now history appears to repeat itself, with many investigators promoting an improved version involving day 5/6-blastocyst trophectoderm biopsy in place of day-3 embryo biopsy and 24-chromosome copy number analysis by various available technologies in place of fluorescence in-situ hybridization (FISH).

All above noted articles uncritically accept that the earlier PGS failure was due to technical shortcomings of day-3 biopsies and chromosomal analyses by FISH. They assume that these shortcomings are remedied by the utilization of trophectoderm biopsy and new 24-chromosome copy analyses, and that PGS now fulfills its presumed destiny of improving in vitro fertilization (IVF) outcomes.

But what if PGS did not fail because of technical shortcomings? What if it failed because PGS should not be applied indiscriminately to every patient or because embryo selection by PGS statistically simply does not work in older women or with low ovarian reserve? Wouldn’t we then only repeat the same mistakes all over?

Scott’s group presented three papers in support of the new PGS. All three papers are fundamentally flawed because their outcome analyses are not based on intent to treat and involve only patients who do reach embryo transfer (ET). With the new PGS, many patients, however, do not: some because their embryos do not make it to days 5/6; others because all tested embryos are aneuploid. Those, quite obviously, are adversely selected. Conversely, those who do make it to ET are favorably selected. Reported results, therefore, are only achieved in a highly favorably selected patient population, and should not be considered representative of all IVF.

Despite favorable patient selection, Scott et al. still transferred 1.9 and 2.0 embryos, respectively, in PGS and control groups. With 2-ET the authors achieved implantation rates of 66.4% vs. 47.9% and delivery rates of 84.7% vs. 67.5% (3). Results in unselected patients would, however, be very different!

PGS may indeed work in patients with best pregnancy chances, as suggested by Scott et al., further increasing pregnancy rates by up to approximately 25%. This is a point we have made before (4). We, however, strongly caution against prematurely concluding that PGS should also be applied to less favorable patients. We are not alone in calling for caution (5). Because of failure to reach embryo transfer, poorer prognosis patients will, likely, fail to improve pregnancy chances equally well. They often are also prematurely driven into egg donation after repeatedly not making it to day-5 ET, though would still have conception chances with day-3 ET (4).

Whether PGS in association with routine IVF is, therefore, really alive and very well remains to be seen.

Norbert Gleicher, M.D., Vitaly A. Kushnir, M.D., David H. Barad, M.D., M.S.
Center for Human Reproduction (all authors), New York, New York
Foundation for Reproductive Medicine (N.G., D.H.B), New York, New York


1. Meldrum DR. Introduction: Preimplantation genetic screening is alive and very well. Fertil Steril 2013;100:593-4.

2. Mastenbroek S, Twisk M, van der Veen F, Repping S. Preimplantation genetic screening: a systematic review and meta-analysis of RCTs. Hum Reprod Update 2011;17:454-66.

3. Scott RT Jr, Upham KM, Foreman EJ, Hong KH, Scott KL, Taylor D, et al. Blastocyst biopsy with comprehensive chromosome screening and fresh embryo transfer significantly increases in vitro fertilization implantation and delivery rates: a randomized controlled trial. Fertil Steril 2013;100:697-703.

4. Gleicher N, Kim A, Weghofer A, Barad DH. Lessons from elective in vitro fertilization (IVF) in, principally, non-infertile women. Reprod Biol Endocrinol 2012;10:48.

5. Mastenbroek S. One swallow does not make a summer. Fertil Steril 2013;99:1206.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2013.09.019

The authors respond:

The authors make an important point that cannot be overemphasized. The studies done to date have not specifically included poor responders or couples having reduced embryo quality, so we should not use results found in favorable cases to imply that similar outcomes would be obtained in more difficult patients. The authors also emphasize that some embryos may be lost due to lack of progression to day 5 or 6 in culture. There has been no study to verify that there are embryos capable of developing into viable implantations when transferred day 2 or 3 that would fail to continue development in vitro, and the reference quoted by the authors provides no information to answer that question. However, exposure to in vivo conditions could improve embryo quality over the remaining 2 to 4 days that embryos would otherwise be in the laboratory, and studies showing improved implantation when poor responders have a day-2 versus a day-3 transfer support the possibility of such an in-vivo benefit. Quality of the laboratory and perhaps even of the maternal environment would influence those outcomes. Differing rates of blastocyst development with varying laboratory techniques also support those conclusions. Manipulation and removal of trophectoderm cells could impact a suboptimal embryo while having minimal or no impact on an embryo emanating from a better prognosis patient. For these reasons, in our programs we do not generally recommend PGS for those couples and would rather transfer their embryos on day 2 or 3. To choose among cleavage-stage embryos for transfer, metabolomics, proteomics, morphology and/or time-lapse evaluation of early-cleavage parameters will be needed. Fortunately, the risk of multiple pregnancies is lower for poor-prognosis couples.

We do have good information regarding outcomes for normal women. Forman et al. showed that of non-obese women under age 43 (with a mean age of 35) having normal ovarian reserve, 85% (175/205) had at least two embryos adequate for biopsy on day 5 or 6, 8% had non-elective single embryo transfer, and only 11 (5%) had no blastocyst for transfer or vitrification (1). The high rate of ongoing pregnancy (61%) with transfer of a single, chromosomally normal blastocyst implied a minimal impact of biopsy and was equivalent to transfer of two untested blastocysts. That study was fully transparent in providing a CONSORT diagram, with only 1% of patients cancelled for poor response. The study was randomized based on a sample size calculation, and results were reported by intention to treat analysis.

In a further study with a powerful design with embryo pairs undergoing biopsy or no treatment and using DNA imprinting to track which embryos implanted (2), those same investigators were able to show in a favorable group of patients that there was no apparent impact of trophectoderm biopsy in contrast to almost a 40% reduction of embryo viability with cleavage-stage biopsy. Their findings gave strong support to the concept that removal of trophectoderm cells in favorable patients has minimal or no impact on the embryo. In sharp contrast, removing a single blastomere on day 3 had a pronounced negative effect. It is therefore easy to understand, in addition to the inherent errors with fluorescence in-situ hybridization (FISH) testing and the limited number of chromosomes tested, why no randomized study has been able to show a benefit of cleavage-stage biopsy for PGS. Randomized studies are essential because different fertility potential of study and control groups and reporting of results following clusters of favorable outcomes can readily produce spurious results, particularly with very small data sets.

Schoolcraft et al. reported a case-control study of couples with a mean age of the female partner of 38 with an ongoing pregnancy rate of 60% with transfer of a single, chromosomally normal blastocyst (3). In an ongoing randomized trial by those same investigators (4), women with a mean age of 39 were found to have a significantly higher viable implantation rate following PGS and vitrification (61 vs 41%, p < 0.05), in spite of transfer of significantly fewer embryos (p < 0.01), and with a significant reduction in miscarriage (20 vs 0%, p < 0.05). However, considering the mean AMH and AFC values reported, these older women were predominantly good responders.

As emphasized in my introduction, even if the cumulative pregnancy rate without comprehensive chromosome screening (CCS) approached the success rate with CCS, the reduction of multiple pregnancies, spontaneous abortions, and avoidance of futile transfers would more than offset the costs of CCS.
As also emphasized in my introduction and essentially all PGS papers, the most important complications of in vitro fertilization (IVF) have been due to multiple pregnancy, which can be severe and even fatal to the mother or her offspring. The risk of multiple pregnancies is greatest in normal responders, who produce multiple blastocysts. Applying CCS to those couples, as in the studies reported above, will have a very favorable impact on the morbidity, mortality, and excessive health care costs attributed to IVF, by allowing transfer of a single, chromosomally normal blastocyst.

Finally, it has been well documented that dropping out of treatment due to inability to cope with repeated failures is the single most important factor limiting the ultimate chance for success with IVF. By avoiding cycles with transfer of embryos that are unable to implant or result in miscarriage, PGS will contribute greatly to those couples’ eventual chance of taking home a healthy baby.
It is important to point out that the results reported above were generated from high quality laboratories. Extended embryo culture requires close attention to many details and rigid quality control. Equivalent results cannot be expected in every IVF facility.

In the publications quoted by the authors, I was unable to find any suggestion that PGS would apply to all patients. We should make it very clear that data to date has been generated in women of moderate to advanced age with normal ovarian reserve. It may turn out that CCS will not be helpful in poor responders or that optimal outcomes will be attained by applying other diagnostics or a combination of CCS and other technologies. The key is that for each of these technologies, including CCS, it will be important to specifically validate the technology in the clinical setting where it will be applied. We (RTS) are currently conducting a randomized trial in poor responders to assess whether CCS has a role in those patients.

The authors were correct in their criticism of the lack of adequate study prior to widespread adoption of day 3 PGS using FISH. In a response to a previous letter regarding day 5/6 PGS using CCS (5), one of us (RTS) replied: “Has any technology in the history of assisted reproduction ever been this well validated before widespread utilization?”

David R. Meldrum, M.D.
Reproductive Partners Medical Group, Redondo Beach, California
Richard T. Scott, Jr., M.D.
Reproductive Medicine Associates of New Jersey, Basking Ridge, New Jersey
William B. Schoolcraft, M.D.
Colorado Center for Reproductive Medicine, Lone Tree, Colorado


1. Forman EJ, Hong KH, Ferry KM, Tao X, Taylor D, Levy B, et al. In vitro fertilization with single euploid blastocyst transfer: a randomized controlled trial. Fertil Steril 2013;100:100-7 e1.

2. Scott RT, Jr, Upham KM, Forman EJ, Zhao T, Treff NR. Cleavage-stage biopsy significantly impairs human embryonic implantation potential while blastocyst biopsy does not: a randomized and paired clinical trial. Fertil Steril 2013;100:624-30.

3. Schoolcraft WB, Katz-Jaffe MG. Comprehensive chromosome screening of trophectoderm with vitrification facilitates elective single-embryo transfer for infertile women with advanced maternal age. Fertil Steril 2013;100:615-9.

4. Schoolcraft W, Surrey E, Minjarez D, Gustofson RL, Scott RT, Katz-Jaffe MG. Comprehensive chromosome screening with vitrification (CCS) results in improved clinical outcome in women > 35 years: a randomized control trial. Fertil Steril 2012;98:1.

5. Scott RT, Forman EJ, Treff NR. Reply of the authors. Fertil Steril 2013;100:E7-8.

Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2013.09.020




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