Ultrastructure of preimplantation human embryos co-cultured with human ampullary cells

Ova with two pronuclei were co-cultured with established human ampullary cell lines and various stages of preimplantation embryonic development were monitored by Nomarski optics and then assessed by transmission electron microscopy (TEM). Fifteen embryos ranging from the 2-cell stage to blastocyst hatching were examined for normal and abnormal features. Their ultrastructure was similar to that of embryos cultured in Whittingham's T6 medium, reported previously. Seven embryos were evidently morphologically normal and showed good organization of fine structure. Most cellular organelles underwent progressive changes during early development. There was evidence of enhanced embryonic genome activation at the 8-cell stage. Invariably, all embryos had few too many fragments, some internalized, which were later segregated into the blastocoele or found outside the trophoblast of the late morula and blastocysts. Six grossly 'normal' embryos assessed by Nomarski had multiple nuclei of various dimensions, which highlights the subjectivity of embryo assessment in the IVF laboratory. Incomplete incorporation of chromatin into nuclei and formation of micronuclei were evident in some blastomeres. The results are discussed in relation to early embryonic loss, prevalent in IVF. Significant events reported include the detection of centrioles at the 8-cell stage, cavitation of the early blastocyst and the initiation of blastocyst hatching visualized by TEM.