Distribution tree of COCs involved in the study. A total of 212 COCs were retrieved from the 15 PCOS patients. Except for 6 COCs which are atretic or with fractured zones pellucidae were discarded, there have 3 GV stage COCs, 30 MI stage COCs, and 173 MII stage COCs. On Day 1 (16–18 hours after insemination), 130 CCs separated from oocytes with normal fertilization (2PN) and 36 CCs separated from mature oocytes with abnormal fertilization (MPN) were classed into a “CC2PN” and “CCMPN” group, respectively. On Day 3, 54 of 127 embryos that developed from oocytes with normal fertilization (2PN) were transplanted or frozen, and their corresponding CCs were classified into six subgroups randomly. The other 73 embryos were cultured to the blastocyst stage. Cumulus cells from oocytes yielding blastulas after 5/6 days in vitro culture were classified as the “CCB+” group (n = 37), and cumulus cells from oocytes that stopped developing at the embryo stage after Day 6 were divided into “CCB-” groups (n = 36). COC, cumulus-oocyte-complex; CCGV, cumulus cells from GV oocyte; CCMI, cumulus cells from MI oocyte; CCMII, cumulus cells from MII oocyte; CC0PN, cumulus cells from oocyte which formed no pronuclei (0PN) after fertilization; CC2PN, cumulus cells from oocyte which formed two pronuclei (2PN) after fertilization; CCMPN, cumulus cells from oocyte which formed multi pronuclei (MPN) after fertilization; CCWLGE, cumulus cells from oocyte yielding a weak or low grade embryo at Day3; CCTQE, cumulus cells from oocyte yielding a top quality embryo at Day 3; CCB-, cumulus cells from oocyte which stopped development at the embryo stage at Day 5/6; CCB+, cumulus cells from oocyte yielding a blastocyst after 5/6 days of in vitro culture.