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.