[Developmental arrest of fertilized human oocytes in the pronuclear stage after in vitro fertilization (IVF)].

Developmental arrest of 18 ova (about 5%) of 362 fertilized oocytes showing formation of two pronuclei was observed after in-vitro fertilization. In 7 ova the pronuclei were still visible 40 hrs after insemination. Five ova were degenerated after formation of the pronuclei. Cytological analysis of the ova revealed that the arrest of development had occurred at different stages of the cell cycle (interphase to metaphase of the first mitotic division) with one ovum being characterized by a tetraploid chromosome set. Asynchronous development of the pronuclei, which is obviously a cause of early developmental arrest, was observed in 4 ova. According to our observations we would rather transfer fertilized oocytes after cell cleavage (in the 2- to 6-cell stage) than in the pronuclei stage.