To the Editor:
We wish to express concern about the design, analysis and conclusions reported in the article by Moschini et al. (1). This study compares the efficiency of an oocyte IVM medium (Medicult) to a cleavage-stage embryo culture medium (Sage IVF), for the in vitro maturation (IVM) of denuded oocytes that have failed to respond to gonadotropins in a standard IVF cycle (rescue IVM). We have a number of objections to this study:
1) The authors have attempted to examine the efficiency of an oocyte IVM medium that is not designed and is not appropriate for culture of oocytes lacking cumulus cells (denuded oocytes). Oocyte IVM media are intended for the culture of intact cumulus-oocyte complexes (COC). As COC contain 1000-5000 cumulus cells, but just one oocyte, IVM media are designed principally to meet the nutritional needs of the somatic cells. Hence, IVM media are complex media capable of supporting the high metabolic requirements of the COC (e.g., very high glycolytic activity), whereas cleavage media are designed for the low metabolic needs of the early embryo (e.g., utilize glucose poorly) (2). As such, one should not expect IVM media to be suitable for culturing denuded oocytes, so it is perplexing that the authors would choose to undertake such a comparison.
2) This study is substantially underpowered, which has led the authors to make a classical type-II statistical error in their conclusions. There are just 24–38 oocytes in each arm of this study. Not surprisingly, with such low numbers, the authors have been unable to detect a statistical difference between treatments. A simple power analysis (α=5%, β=10%) on the GV to MII group reveals that 664 oocytes would have been required to correctly conclude no actual improvement with the IVM medium. Clearly such numbers are not practical so the decision to undertake the trial was flawed. Instead, the authors come to the inappropriate conclusion that the IVM medium is not better than cleavage medium, when in fact, with so few oocytes, they would be unable to detect such a difference if it were to exist.
3) Finally, the authors come to the disturbing conclusion that the greater potential application of IVM is to rescue the currently unusable immature oocytes retrieved in standard IVF, rather than IVM in unstimulated cycles. There is now ample evidence in the literature that immature oocytes collected in standard IVF cycles are inherently abnormal. The authors in fact cite many examples of this evidence, but not perhaps the most compelling. Jones et al (3) conducted a comprehensive microarray analysis of rescue IVM human oocytes vs. in vivo matured oocytes. The rescue IVM oocytes showed grossly aberrant gene expression (2766 genes), consistent with features such as chromosomal misalignments, alarming rates of oocyte and embryo aneuploidies (4, 5) and very limited oocyte developmental competence post-IVF. These findings should not be surprising, as these rescue IVM oocytes have failed to respond to the ovulatory gonadotrophin stimulus in standard IVF. While rescue IVM oocytes may be of some use as research material, we feel it is quite inappropriate for the authors to advocate the use of rescue IVM oocytes for the treatment of infertility.
Robert Gilchrist, D.Sc.Agr.1
Michel De Vos, M.D., Ph.D.2
Johan Smitz, M.D., Ph.D.2
Dr. Jeremy Thompson1
School of Paediatrics and Reproductive Health
University of Adelaide
2Centre for Reproductive Medicine and Medical School
Free University of Brussels (VUB)
1. Moschini RM, Chuang L, Poleshchuk F, Slifkin RE, Copperman AB, Barritt J. Commercially available enhanced in vitro maturation medium does not improve maturation of germinal vesicle and metaphase I oocytes in standard in vitro fertilization cases. Fertil Steril 2011; (doi:10.1016/j.fertnstert.2011.03.094).
2. Sutton ML, Gilchrist RB, Thompson JG. Effects of in-vivo and in-vitro environments on the metabolism of the cumulus-oocyte complex and its influence on oocyte developmental capacity. Hum Reprod Update 2003; 9:35-48.
3. Jones GM, Cram DS, Song B, Magli MC, Gianaroli L, Lacham-Kaplan O, Findlay JK, Jenkin G, Trounson AO. Gene expression profiling of human oocytes following in vivo or in vitro maturation. Hum Reprod 2008; 23:1138-1144.
4. Nogueira D, Staessen C, Van de Velde H, Van Steirteghem A. Nuclear status and cytogenetics of embryos derived from in vitro-matured oocytes. Fertil Steril 2000; 74:295-298.
5. Strassburger D, Goldstein A, Friedler S, Raziel A, Kasterstein E, Mashevich M, Schachter M, Ron-El R, Reish O. The cytogenetic constitution of embryos derived from immature (metaphase I) oocytes obtained after ovarian hyperstimulation. Fertil Steril 2010; 94:971-978.
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2011.06.012
The Authors Respond:
We would like to thank Gilchrist et al. for the interest in our recent article, and we welcome their observations and comments. Please allow us to address them individually:
1) As stated in the opening paragraph, our study specifically does not address the “intended” application of enhanced IVM media, the culture of oocytes not previously exposed to gonadotropins. Instead, we compared this complex culture media to our standard culture media, for use in assisting maturation of retrieved immature oocytes following IVF stimulation. We observed the maturation of supernumerary, immature, denuded oocytes from stimulated cycles. It is not uncommon to observe immature oocytes in specialized media in hope of achieving a viable and genetically normal gamete.
2) As for the suggestion that we “substantially underpowered” our study, we agree that larger numbers would have been necessary to detect a 10% difference depending on choice of media. However, given that specialized media such as Medicult IVM was designed to augment maturation, we powered the study expecting to see at least a 50% increase in maturation of immature oocytes using the specialized IVM medium. Our study had an 80% likelihood of finding such a difference and clearly did not note any advantage of culture with the specialized medium.
3) We highlighted several studies that point towards the chromosomally compromised characteristics of IVM oocytes from stimulated cycles, but we agree that the references were not a comprehensive analysis on the subject of IVM and that the Jones (1) article merits mention. As stated in the manuscript, our goal was to evaluate the likelihood of maturation occurring in immature oocytes cultured with a variety of media. We look forward to performing further analysis of the efficacy and safety (the reproductive competence) in clinical practice.
Alan B. Copperman, M.D.1,2
Rose Marie Moschini, M.Sc.1
Richard E. Slifkin, B.A.1
Jason Barritt, Ph.D.1,2
1Reproductive Medicine Associates of New York
New York, New York
2 Department of Obstetrics and Gynecology and Reproductive Science
Mount Sinai School of Medicine
New York, New York
1. Jones GM, Cram DS, Song B, Magli MC, Gianaroli L, Lacham-Kaplan O, et al. Gene expression profiling of human oocytes following in vivo or in vitro maturation. Hum Reprod 2008; 23:1138-44.
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2011.06.013