The prognostic significance of Day 3 embryo cleavage stage on subsequent blastocyst development in a sequential culture system

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 undergoi ng standard protocols and BL transfer after sequential embryo culture in PI 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% (5 6/147), P < 0.0001. The majority of BL, 68.9% (168/244), were observed on D ay 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 si gnificantly greater likelihood of BL development. Embryos containing 4-6 bl astomeres 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 devel opment.