Because the parameters measured by the researchers in this study occur before any embryonic genes are expressed, the results indicate that embryos are likely predestined for survival or death before even the first cell division.
.. Despite their best efforts, though, they have only about a 35 percent success rate. As a result, most women elect to transfer two or more embryos to increase the chance of a live birth.
.. the embryos at first express only genes from the maternally derived egg. By roughly the third day (the eight-cell stage) they begin to express genes specific to embryonic development
.. The researchers found embryos in which some cells were dividing on schedule while others were seemingly stuck, or paused.
.. embryos in which individual cells varied significantly in their cell-division schedules or gene-expression profiles were less likely to become successful blastocysts.
.. Cells that fail to execute some part of this delicate process get out of sync with their neighbors and jeopardize the life of the embryo.
.. “In mice, about 80 to 90 percent of embryos develop to the blastocyst stage. In humans, it’s about 30 percent,” said Reijo Pera.
.. “In addition, about one in 100 mouse embryos are chromosomally abnormal, versus about seven out of 10 human embryos.