There is a cutoff limit in diameter between a blastomere and a small anucleate fragment

Purpose: To document the DNA content of blastomeres/fragments from early human preembryos and to determine if there is a cutoff diameter at which a cell should be considered an anucleate fragment rather than a blastomere. Methods: Surplus embryos from in vitro fertilization were used. Individual cells were measured, fixated, and stained for DNA. Results: In day 2 preembryos, only 2% of cells with a diameter < 45 μm contained DNA, compared with 67% of those ≥45 μm. In day 3 preembryos, 3% of cells < 40 mum contained DNA, compared with 66% of those greater than or equal to40 mum. Conclusions: It is suggested that cells < 45 μm in day 2 preembryos, and < 40 mum in day 3 preembryos should be classified as fragments, and cells larger than this, as blastomeres. This may influence the embryo scoring system for in vitro fertilization. We therefore recommend that cells within this critical range should be measured when scoring preembryos for embryo transfer.