Cleavage rate and morphology of early human embryos obtained after artificial fertilization and culture.

Ovarian follicles were aspirated at midcycle from 193 women admitted to the hospital because of infertility or for legal sterilization. Eighteen women had not received prior hormone stimulation and 175 had been stimulated either with Clomiphene citrate and hCG with hCG alone. Preovulatory oocytes could not be obtained from any of the women in the non-stimulated group, but were obtained from 86 (49%) in the stimulated group. Of these 86, oocytes from 63 women were cultured successfully and from 47 (75%) cleavage occurred. The most advanced stages observed were about 10-cell embryos, but no attempts were made to culture them further. Almost all the oocytes which cleaved were obtained from women in whom the progesterone level started to rise from the basal level within 24 hours of the operation. Eight cleaved oocytes were taken for transmission electron microscopy (TEM). Early cleavage stages showed spheroidal mitochondria with a few peripheral cristae, while the number of elongated mitochondria with transverse cristae increased in later stages. Mitochondria-vesicle complexes, consisting of a vesicle filled with a dense substance and surrounded by 5-15 mitochondria, were observed in early (but not in more advanced) embryos. The complex is probably part of a transport system from the nucleus to the mitochondria. In the later stages, a type of granulated vesicle appeared. Thus, some changes occurred in tact with the degree of development, while no differences could be seen between oocytes with differing cleavage rates.