EFFECTS OF EMBRYO DENSITY AND COCULTURE OF UNFERTILIZED OOCYTES ON EMBRYONIC-DEVELOPMENT OF IN-VITRO FERTILIZED MOUSE EMBRYOS

We have evaluated the effects of embryo density and the co-culture of unfertilized (degenerating) oocytes on the development of in-vitro fer tilized (IVF) mouse embryos, In experiment 1, groups of one, five, 10 or 20 zygotes were cultured in 20 mu l drops of modified human tubal f luid (HTF) medium for 168 h at 38.7 degrees C in 5% CO2 and 95% air, A s the embryo density increased, significantly (P < 0.05) higher rates of embryos reached hatched blastocyst stage, In addition, the time req uired for hatching after IVF was significantly (P < 0.05) shortened by the increase in embryo density, In experiment 2, 10 IVF zygotes were cultured with or without 10 unfertilized (degenerating) oocytes in 20 mu l drops of HTF medium, The rates of IVF embryos that developed to m orula, blastocyst, expanded blastocyst and hatched blastocyst stages w ere decreased significantly (P < 0.01) by culturing embryos with unfer tilized oocytes compared with culturing embryos alone. In experiment 3 , groups of one or 10 IVF zygotes or 10 IVF zygotes plus 10 unfertiliz ed oocytes were cultured in 20 mu l drops of HTF medium and the number of cells per blastocyst was examined at 120 h after IVF, Increasing e mbryo density resulted in a significant (P < 0.05) increase in the num ber of cells per blastocyst. In contrast, the cell number of IVF embry os that developed to blastocyst decreased significantly (P < 0.05) whe n they were cultured with unfertilized oocytes, The results suggest th at in-vitro development of IVF mouse embryos is enhanced by increasing embryo density and is impaired by co-culture with unfertilized (degen erating) oocytes.