The dynamics of in vitro maturation of germinal vesicle oocytes

Escrich, L, Grau, N, de los Santos, M J, Romero, J L, Pellicer, A, Escriba, M J,
Fertil Steril. Nov. 2012 doi: 10.1016/j.fertnstert.2012.07.1116


OBJECTIVE: To evaluate the dynamics of the nuclear maturation (NM) of in vitro-matured (IVM) oocytes and to determine the most favorable duration of meiosis II (MII) arrest in relation to the normal activation response. DESIGN: Experimental. SETTING: University-affiliated infertility clinic. PATIENT(S): Donated immature germinal vesicle oocytes (GV). INTERVENTION(S): The GV underwent spontaneous IVM and the dynamics of NM studied by real-time monitoring. The IVM oocytes were parthenogenetically activated at different MII arrest points and their response assessed. MAIN OUTCOME MEASURE(S): Moment of GV breakdown; extrusion of the first polar body; duration of MI and MII arrest; activation rate (AR) and type. RESULT(S): Two GV populations-early (E-IVM, 18.4 +/- 2.7 hours) and late (L-IVM, 26.3 +/- 3.8 hours) maturing-were defined according to the time required for extrusion of the first polar body. Significantly more E-IVM than L-IVM exhibited a normal activation response (61.3% vs. 34.6%), but AR were similar (average, 88.6%) in both groups. Duration of the GV stage differed between the two groups, but MI arrest (14.0 +/- 0.3 hours) was constant. The E-IVM arrested at MII for at least 4.3 hours displayed significantly lower AR and similar normal activation rates (61.3%) to E-IVM arrested for a shorter time (83.9% vs. 100%). The L-IVM displayed a similar AR (80.8%), but lower normal activation rates than E-IVM (34.6%), regardless of when activation took place. CONCLUSION(S): The success of IVM depends on the NM timing rather than on the length of MII arrest.