Nuclei number in human embryos co-cultured with human ampullary cells.

A study was undertaken to evaluate the effect on nuclei number in human embryos cultured in vitro with primary cell lines of human Fallopian tube epithelium. The development of 203 surplus human embryos, cultured in standard culture medium (Earle's balanced salt solution + 15% A5) with or without ampullary cells, was observed from day 2 to day 5.5 post-insemination. The expanded blastocysts in both culture conditions were analysed for nuclei numbers per blastocyst. Embryos transferred to co-culture at the 2-cell stage had an average of 120.7 nuclei per blastocyst, which was significantly higher than the average of 62.9 nuclei per blastocyst (P = 0.023) for the embryos transferred to co-culture at the 4-cell stage. The embryos cultured in the control medium had an average of 42.1 nuclei per blastocyst, which was significantly less than co-cultured embryos (P = 0.04). Severely fragmented embryos (grades 3 and 4) did not show recovery in co-culture. Our results show that when human embryos are transferred to co-cultures before the 4-cell stage, the blastulation rate and the cell number per embryo increase significantly compared to the embryos cultured in standard culture medium. The possible effect of co-culture on embryonic gene expression is discussed.