Fertilization, cleavage and blastocyst development according to the maturation timing of oocytes in in vitro maturation cycles*

BACKGROUND: This study was to examine the developmental capacity of oocytes collected from an in vitro maturation (IVM) programme according to their maturation time. METHODS: The study included 47 IVM cycles that underwent blastocyst transfer. The patients (n = 38) were primed with 10 000 IU HCG 36 h before their oocyte retrieval. The oocytes were classified into three groups: group 1 (n = 139) where oocytes were matured on day of oocyte collection; group 2 (n = 627) where oocytes were matured on day 1 after IVM; group 3 (n = 163) where oocytes matured on day 2 after IVM. Fertilization, cleavage and blastocyst formation were compared between three groups. RESULTS: Rates of cleavage and blastocyst development in group 3 (72.2%, 96/133; 19.0%, 15/133) were significantly lower than those of group 1 (100%, 108/108; 58.3%, 63/108) and group 2 (91.5%, 487/532; 50.4%, 268/532) respectively (P < 0.01). The number of freezable good quality blastocysts among blastocysts developed from group 1 (52.4%, 33/63) was significantly higher than those from group 2 (35.4%, 95/268) and group 3 (6.7%, 1/15) (P < 0.01). There were 24 clinical pregnancies (51.1%, 24/47) after transfer of the blastocysts and 29 healthy babies were delivered. CONCLUSION: These results suggest that oocytes reaching metaphase II faster in an IVM programme have better embryonic developmental competence.