The potential of early human embryos to form blastocysts, hatch from their zona and secrete HCG in culture.

Early embryos assessed to be unsuitable for transfer to patients or for cryopreservation were cultured either in minimum essential medium (MEM) or in synthetic human tubal fluid (HFT). A significantly higher percentage of embryos developed to blastocysts in MEM (26.5%) than in HTF (14.5%). Serum was not required for blastocyst formation nor for hatching in MEM. HTF containing 1% human cord serum failed to support blastocyst hatching. Haploid (monopronucleate) and diploid (bipronucleate) embryos formed blastocysts and hatched with a similar frequency but triploid (tripronucleate) embryos developed poorly. Human chorionic gonadotrophin (HCG) released by hatched and intrazonal blastocysts was detected between days 7 and 8 after fertilization. The mean total HCG produced by hatched blastocysts by day 14 was 19,500 mIU, but embryos trapped inside their zonae released a mean level of 1550 mIU. Serum was shown to stimulate the output of HCG from both hatched and intrazonal blastocyst tissues. Free beta- and alpha-subunits of HCG were not released by developing blastocysts, but low levels of beta-HCG were produced by some embryonic tissues between days 12 and 14 when degenerative changes were observed.