Micromanipulation of human gametes and embryos: ooplasmic donation at fertilization VIDEO.

Abstract

It is well known that human embryos may from anomalies both in vitro and in vivo. Progress through the preimplantation stages can be marked by multiple nuclei in some or all blastomeres, the formation of numerous fragments of varying size and organized in different patterns, and by arrests in development at virtually any stage. Various parameters have been offered as markers of the success of embryo growth and its culmination in implantation. Some of these involve characteristics in the follicles such as size, steroid output, properties of cumulus cells and others. Most involve studies on embryos in vitro, analysing timing of cleavage, blastomere structure, chromosome complement and timing of blastulation. More recently, characteristics in the structure of the pronuclei or of the ooplasm have been introduced. Certain dysmorphisms in the oocyte may predict implantation failure (Van Blerkom et al., 1995), whereas other characteristics hint at polarity in the pronucleate egg to make a detailed forecast of the likelihood of particular embryos achieving implantation (Scott and Smith, 1998). Cytogenetic studies using fluorescence in-situ hybridization of all cells from whole embryos have shown that certain morphological markers such as pronuclear and blastomere size can predict anomalies with high accuracy (S.Munne and J.Cohen, manuscript submitted). Such studies may ultimately help embryologists to assist in selecting embryos for replacement of cryopreservation. Virtually all of these issues remain to be proven in large-scale prospective controlled trials, yet there is much optimism that some of these parameters will be applied, and some of them demand no more than examining the eggs in vitro. Another approach to improving the growth of human embryos is to interfere physically or embryologically with them in order to avert an impending problem or to set them on the correct pathway to full-term development. In a sense, changing culture medium is one form of manipulation. More relevant to the present video, intrusive methods such as assisted hatching, zona removal, excising cytoplasmic fragments, and ooplasmic donation (Cohen et al.,