Embryonic development and blastocyst implantation following in vitro fertilization and embryo transfer

A sensitive and specific radioimmunoassay was used to measure human chorionic gonadotropin (hCG) excretion in serial overnight urine samples in women having embryo transfer, in an in vitro fertilization program. Elevated hCG excretion suggestive of blastocyst implantation was detected in 17 of 121 women studied. When the results were corrected for interference by luteinizing hormone and other immunoreactive substances, implantation was detectable 8 to 9 days after fertilization in 20% of conceptual cycles, in 80% by days 12 to 13, in 93% by days 14 to 15, and in 100% by days 16 to 17. From a life table of human embryo development in culture, it was estimated that 37% of four-cell and 43% of eight-cell embryos reached the blastocyst stage. On the basis of these estimates and the elevated hCG from implanting blastocysts, it was concluded that 60% to 65% of uterine blastocysts either failed to implant or failed to produce measurable hCG.