Culture of human preimplantation embryos to the blastocyst stage: a comparison of 3 media.

Following culture for 2 days in Earle's balanced salt solution (EBSS), human embryos which remained after transfer were cultured in one of 3 media for 4 days, from the 2- to 4-cell stage to the blastocyst stage. Sibling embryos were divided equally between treatments. Throughout the 4 day culture period, embryos were assessed for morphology and development, as well as uptake and production of energy substrates. Cell numbers in the inner cell mass and trophectoderm were determined for embryos which reached the blastocyst stage. No significant effect was observed in the extent or rate of development to the 8-cell, morula or blastocyst stage between treatments. Uptake of pyruvate was related to concentration in the medium and no differences in glucose uptake were observed between media. Endogenous energy metabolism, as measured by lactate production, was significantly higher in Ham's F12 than in EBSS from day 3.5 onwards. Blastocyst cell numbers were also increased; 79.6+/-7.7 in Ham's F12 (n=17) and 57.8+/-5.2 in EBSS (n=19), p<0.05. Of the embryos which reached the blastocyst stage by day 5, 36% (14/25) had degenerated by day 6 in EBSS compared to only 19% (5/27) in Ham's F12 (p=0.06). Slightly higher rates of embryo survival between day 5 and 6 in Ham's F12 may account for the observed increase in blastocyst cell number. The results do not suggest that improved embryo development can be obtained using human tubal fluid or Ham's F12, in preference to EBSS during early cleavage stages, but the use of Ham's F12 may improve embryo survival at later stages of development.