Effects of culture milieus on the development of mouse blastocysts in vitro.

Various culture milieus were examined for their support of mouse blastocyst development. Two important variables were the time at which human cord serum was added to the medium and the concentration of amino acids. In the best medium. Eagle's Minimum Essential Medium (fortified with six times the usual amino-acid concentration plus 20 percent fetal bovine serum, replaced after 48 hr with human cord serum), 83 percent of the blastocysts shed the zona pellucida, 58 percent developed to the early egg cylinder stage, 42 percent to the advanced egg cylinder stage and 22 percent attained the primitive streak stage after 6 to 8 days of culture.