The dynamics of in vitro maturation of germinal vesicle oocytes

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.

Experimental.

University-affiliated infertility clinic.

Donated immature germinal vesicle oocytes (GV).

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.

Moment of GV breakdown; extrusion of the first polar body; duration of MI and MII arrest; activation rate (AR) and type.

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.

The success of IVM depends on the NM timing rather than on the length of MII arrest.