Involvement of programmed cell death in preimplantation embryo demise.

Fragmentation is frequently observed in animal and human embryos obtained via in-vitro fertilization (IVF), and is known to be associated with decreased pregnancy rates and poor survival following cryopreservation. We postulate that embryo fragmentation is a consequence of activated programmed cell death (PCD) and subsequent apoptosis and discuss evidence of morphological, histological and biochemical features compatible with the occurrence of PCD in preimplantation embryos. If PCD is an underlying cause of the high incidence of the fragmentation seen in human pre-embryos, it remains to be determined whether this is reflective of the natural incidence of lethal chromosomes in the human population or due to the IVF procedure and culture conditions.