Effects of medium composition on murine and human blastocyst formation and hatching rate

Murine two-cell embryos (n = 5573) were cultured for 96 hr in human tubal fluid (HTF) medium (n = 2709) or alpha modification of minimum essential medium (MEM; n = 2864) through the hatched blastocyst stage from mid-1990 to mid-1991. An additional 373 embryos were cultured in MEM or HTF with 0, 1, 5, or 10 ng/ml E. coli endotoxin. A total of 17 patients had supernumerary embryos simultaneously cultured in HTF (n = 48) or MEM (n = 61). Additionally, pregnancy rates were compared for July to December 1990, when MEM was used as growth medium, and for July to December 1989, when HTF was used.

Blastocyst formation was higher (P < 0.001) for murine embryos cultured in MEM (blasts = 95%) compared to HTF (blasts = 70%). When cultured with endotoxin, blastocyst formation was higher (P < 0.01) for embryos cultured in MEM compared with HTF for controls and at each endotoxin level. No difference in human blastocyst development was observed in HTF and MEM. However, more MEM-cultured blastocysts were cryopreserved (P < 0.05). There also was a lower spontaneous abortion rate and a higher multiple gestation rate when embryos were cultured in MEM.

Thus, MEM may result in healthier blastocyst development, especially when culture conditions are substandard, although this is not an acceptable substitution for meticulous technique.