Fig. 1.

Morphology of human fertilized embryos, blastocysts, ICM and human ESCs. a, b Discarded low-quality fertilized embryos that did not meet the embryo transfer criteria in IVF or ICSI cycles. c Blastocyst on day 6.5 before ICM isolation. d Isolated ICM. e Attached ICM on human foreskin fibroblast feeder layer on day 1. f Primary colony of human ESCs on day 14. g Colony of human ESCs at passage 2. h Colony of human ESCs at passage 20