Department of Obstetrics and Gynecology, Women's and Children's Hospital, University of Southern California Keck School of Medicine, Los Angeles, California 90033, USA. drboostanfar@hotmail.com
PURPOSE: To determine prognostic significance of blastomere number on Day 3 of culture upon subsequent blastocyst (BL) development. METHODS: A retrospective analysis was conducted in 37 IVF subjects undergoing standard protocols and BL transfer after sequential embryo culture in P1 and BL media. RESULTS: Of Day 3 embryos containing 7 or more blastomeres, 68.9% (186/270) developed into BL compared to embryos containing 4-6 blastomeres, 38.1% (56/147), P < 0.0001. The majority of BL, 68.9% (168/244), were observed on Day 5. Extended Day 6 culture represented 31.1% (76/244) of all BLs. CONCLUSIONS: The observation of 7 or more blastomeres on Day 3 yielded a significantly greater likelihood of BL development. Embryos containing 4-6 blastomeres are still relatively likely to progress to a BL. Extended culture to Day 6 still yields a significant proportion of BL. Cell cleavage stage on Day 3 appears to be a useful prognostic indicator of subsequent BL development.