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Human Preimplantation Embryo Selection

2007 Edition, September 26, 2007

Complete Document

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Active, Most Current

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ISBN: 978-0-415-39973-9
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Product Details:

  • Revision: 2007 Edition, September 26, 2007
  • Published Date: September 26, 2007
  • Status: Active, Most Current
  • Document Language: English
  • Published By: CRC Press (CRC)
  • Page Count: 386
  • ANSI Approved: No
  • DoD Adopted: No

Description / Abstract:


Assisted reproductive technology (ART) is a numbers game, with permutations that involve the transfer of multiple embryos . . . but the most important number in IVF is of course the number one. One embryo, one sac, one fetus and one healthy baby - the ability to choose just one embryo that will lead to the successful birth of a baby is what we all crave in our profession. Seeking just this is the name of the game, the "Holy Grail of IVF", as suggested by some of the authors in this book.

The early pioneers of human IVF very quickly observed that not all gametes and embryos had the same potential to establish an ongoing pregnancy, and only a small proportion of oocytes that fertilized in vitro was truly viable. This was quickly followed by noting that, contrary to established experience in animal models such as the mouse, there is an obvious diversity in human embryo morphology and implantation potential. Although a correlation could be seen between outcome and morphological phenomena such as fragmentation, it was generally accepted that aesthetic appreciation – ‘embryonic looks' - could be deceiving, and even the ‘ugliest' embryo of a cohort can sometimes develop into a beautiful healthy baby.After 30 years of clinical IVF treatment, we have learned a great deal about human embryos - but there is still so much left to explore.

The absence of absolute criteria that can predict the implantation potential of an embryo brings to mind the proverbial principle illustrated by the threesome of the Japanese Wise Monkeys - ‘to see no evil, hear no evil, and to speak no evil'. The practice of blindly compensating for lack of appropriate embryonic viability testing by transferring large groups of embryos is now all but gone; the debate surrounding embryo viability has changed instead to one of aptitude – the partial failure of new tests to predict implantation has become the norm. This notion has recently been transformed into a new and exciting science, and the search for the ultimate test has begun: the race is on to achieve the happy retirement of two words: ‘success rate'.

This book was planned as a means of exploring this new and exciting science, and experienced authors who specialize in embryo testing were invited to contribute their expertise. Some of the authors have their background in basic science, other are dedicated to clinical IVF; they all share the common goal of finding this ‘holy grail' with differing approaches and strategies. Our aim was to produce a book that is comparable to a peer-reviewed work, and the authors graciously allowed us to mingle with their text as editors, patiently providing explanations and further data if it was required. Although it is difficult to cover all aspects of gamete and embryo testing in one text, we tried to make it as comprehensive and up to date as possible.

It is divided into four main sections, with chapters dealing with morphology determinations, immunology and metabolism, genetic aberrations, and pre-fertilization parameters.With respect to morphology assessment, there appears to be no real consensus on how to grade human embryos based on their morphology, and it is therefore relatively easy to criticize this most basic tool. It is generally accepted that there is a correlation between cell number and implantation, yet the absolute nature of this correlation is unknown; prospectively randomized trials have never been contemplated in order to determine the real value of morphological parameters or embryo development rate. We feel that use of microscopy is not over, and the morphology debate is becoming of increasing interest, with obvious but ethically challenging work yet to be undertaken.

The second section on embryo metabolism offers an exciting glimpse into the feasibility of scoring embryos by examining spent culture media, using non-invasive tests. Although large randomized trials have not been carried out in this area of research, retrospective data shows promise, and more research is needed to expand the use of this tool for embryo assessment. The third section of the book explores ways of assessing the genetic status of embryos. Some conditions such as aneuploidy and mosaicism may be associated with adverse conditions during follicular growth and gamete preparation, and also correlated with clinical outcome. Cell analysis using gene expression or imprinting are exciting approaches that may one day be available as clinical tools. Mutations in mitochondria, or changes in their patterns of activity provide another potential tool for single cell or whole embryo analyses. The fourth and final section covers examples of pre-fertilization parameters: aspects of sperm function, including DNA and centriolar integrity, and investigations of follicle-specific factors that influence oocyte competence.