Early cleavage of in-vitro fertilized human embryos to the 2-cell stage: a novel indicator of embryo quality and viability.

A number of non-invasive methods have been proposed to evaluate embryo viability in human in-vitro fertilization programmes. In addition to biochemical analyses, a common method for the selection of embryos prior to transfer involves assessment of embryo quality and morphology. We propose a new method to evaluate embryo viability based on the timing of the first cell division. Fertilized embryos that had cleaved to the 2-cell stage 25 h post-insemination were designated as 'early cleavage' embryos while the others that had not yet reached the 2-cell stage were designated as 'no early cleavage'. In all cases the early cleavage embryos were transferred when available. Early cleavage was observed in 27 (18.9%) of the 143 cycles assessed. There were significantly (chi2 = 4.0; P = 0.04) more clinical pregnancies in the early cleavage group, 9/27 (33.3%), compared with the no early cleavage group, 17/116 (14.7%). No difference was found when comparing key parameters (age, stimulation protocol and semen characteristics) of couples belonging to both groups, pointing to an intrinsic property or factor(s) within the early cleaving embryos. We propose 'early cleavage' as a simple and effective non-invasive method for selection and evaluation of embryos prior to transfer.