Ultrastructural evaluation of 8–16 cell human embryos cultured in vitro

The fine structure of eight human embryos cleaving in culture are described. Preovulatory human oocytes aspirated at diagnostic laparoscopies were fertilized and developed in vitro by methods which produced normal pregnancies. Three 8-cell and five 10–16 cell embryos showing delayed cleavage were fixed, serially sectioned and examined to determine whether the embryos were developing normally or otherwise.

The organization of two 8-cell embryos was apparently normal while the other embryos showed varying aspects of abnormal development. Most blastomeres contained organelles normally present in human ova and their fine structure closely resembled those of comparable mammalian embryos. Nearly all the cellular components encountered in early mammalian embryos were observed. Certain morphogenetic changes were also noted during early cleavage involving nuclei, smooth endoplasmic reticulum and mitochondria.

Both normal and abnormal features of the embryos are reported. Multi-nucleated blastomeres and partial fragmentation were commonly seen in abnormal embryos. The importance of ultrastructural evaluation of embryos in an in vitro programme is revealed in this investigation.