The probability of abnormal preimplantation development can be predicted by a single static observation on pronuclear stage morphology

This retrospective study was undertaken to determine whether further develo pmental progression of two-pronucleated (2PN) zygotes can be predicted by a single, non-invasive examination of pronuclei, with the use of criteria ba sed on the number and distribution of nucleolar precursor bodies in each pr onucleus. The normal range of pronuclear variability was defined by analysi s of zygotes giving rise to embryos transferred in 100%-implantation cycles (pattern 0). Morphological patterns differing from pattern 0 were classifi ed as patterns 1-5. The frequency of developmental arrest of pattern 0 zygo tes was only 8.5% as compared with 31.6, 21.9, 30.0, 20.5 and 24.1% for pat terns 1-5 respectively. Relationships of pronuclear patterns with blastomer e multinucleation and cleaving embryo morphology were. also noted. Clinical pregnancy was achieved in 22 of 44 (50%) treatment cycles in which at leas t one pattern 0 embryo was transferred, but only in two of 23 (9%) cycles i n which only pattern 1-5 embryos were transferred. These data present new e valuation criteria which can be used to predict the developmental fate of h uman embryos as early as the pronuclear stage, without requiring repeated o bservations or an exact timing of pronuclear zygote inspection. Further pro spective study is needed for clinical validation of these criteria.