Selecting The Best Embryo For Transfer
At the present time, deciding which embryo to transfer is based upon the best available information. Embryologists carefully observe and record the daily progress of each embryo in culture, with specific attention to the number of cells composing each embryo, symmetry of the blastomeres (embryonic cells), presence or absence of cell fragments, and the texture of the cytoplasm within the cells composing each embryo. Later in the development of the embryo, the embryologist notes the presence or absence of a cavity within the embryo termed a blastocoel, the number and architecture of the cells that will later become the placenta, and the size of the cluster of embryonic cell network termed the “inner cell mass”. Based upon accumulated data, observations, and scientific investigations in reproductive medicine over the past three decades, the embryologist selects the embryo or embryos for transfer.
We have witnessed exciting technological advances, which now enable us to biopsy, each individual embryo and search for selected genetic defects (PGD), or comprehensively screen the embryo for a large number of genetic abnormalities (PGS). This technology, when used, allows for transfer of embryo(s) with normal chromosomal content, thereby decreasing miscarriage rates and at least theoretically increasing pregnancy rates. While we have seen consistent data showing reduced miscarriage rates through application of these technologies, we have not seen consistent improvement in IVF pregnancy rates following PGS. Many suspect that the embryo biopsy, because it is invasive, may adversely affect the embryo leading to reduced prospects for implantation.
A recent publication looks at a considerably less invasive approach to obtaining genetic information about the embryo. Researchers in England and Italy have recently been able to obtain fluid from the early embryonic cavity (blastocoel) and analyze that fluid for DNA. They were able to obtain cell free DNA from the embryo in 90% of the embryos sampled, and in some cases chromosomes were identified in the laboratory utilizing currently available technology. While these are very early studies, this is an exciting development since it holds some promise to provide genetic information about the embryo without the need to remove an embryonic cell. Chromosomal analysis of fluid from the blastocoel could potentially enable us to select the best embryo for transfer with the benefits higher pregnancy rates and lower miscarriage rates. If this technology enables us to get consistently accurate, comprehensive, non-invasive, genetic information about the embryo, it would constitute a major breakthrough in reproductive medicine