Comparison of Morphokinetic Characteristics of Embryos Derived from in-vitro Matured Oocytes Aspirated at Metaphase-I Stage and in-vivo Matured Sibling Oocytes in Stimulated ICSI Cycles - AWARD NOMINEE

Introduction

Despite triggering for final maturation, some of the retrieved oocytes in IVF treatments are immature: either retaining an intact GV or at a transient metaphase I (MI) stage. The latter frequently complete meiotic maturation spontaneously in vitro allowing delayed ICSI. Time Lapse monitoring enables assessment of the impact of this deferred maturation on embryo development.

Aim

To compare early morphokinetic variables and outcome of embryos derived from in vitro and in vivo matured sibling oocytes in stimulated IVF-ICSI cycles.

Materials and methods

All ICSI cycles performed in 2015-2016 in which at least one in vitro matured oocyte was injected & the embryos cultured in time lapse monitoring incubator (EmbryoScope) were retrospectively assessed (1545 injected oocytes in 169 cycles of 149 patients). Fertilization rates & morphokinetic parameters were compared for 285 MI oocytes, after adjusting individual measurements for delayed injections, to those of 1260 sibling oocytes aspirated at the MII stage in the same cycles. Timing of second PB-extrusion, PN-fading, first division to 2-cells (t2) & up to the 8-cell stage (t8) were annotated and durations calculated for PN-fading to first cleavage, second cell cycle (CC2= t3-t2) as well as synchrony of the second cleavage cycle (S2=t4-t3). Optimal CC2 was defined as ≥5 hours and optimal S2 as ≤1 hour. Suitability of embryos for transfer/vitrification or biopsy in PGD cycles served as integrative indicators for adequate embryo quality.

Results

Oocytes maturing from MI aspirated oocytes were injected 3.4hrs±1.4 later than their sibling oocytes (range 1-6.8 hrs) and added to the culture slide. In vitro matured oocytes had lower normal (2PN) fertilization rates than MII aspirated oocytes (50.2% vs 68.0%, p<0.001) while aberrant fertilization rates (1PN and 3PN) were similar (8.8% vs 6.8%, p=0.25). Early key developmental events were significantly delayed: PB extrusion (5.4hrs±3.0 vs 3.9hrs±1.8), PN fading (27.2hrs±4.7 vs 25.1hrs±4.2), t2 (30.1hrs±6.3 vs 28.2hrs±5.8), t3 (38.9hrs±7.2 vs 37.3hrs±6.5) and t4 (42.8hrs±7.5 vs 40.3hrs±6.5), in in-vitro and in-vivo matured oocytes, respectively (p< 0.001 for all).

Timing of later cell divisions (t5-t8), PN fading-t2 interval, and proportion of embryos with optimal CC2 and S2 were not significantly different. In 108 non PGD cycles, only 25.6% of injected in-vitro matured oocytes resulted in embryos eligible for ET/ vitrification vs 42.5% of the MII oocytes (p<0.001) and in 61 PGD cycles 41.3% vs 61.4% (p<0.001) developed to embryos suitable for biopsy. Currently our data is not sufficient for comparing pregnancy rates.

Conclusion

Time lapse monitoring, allowing precise morphokinetic timing, suggests that failure to complete maturation in-vivo entails a disrupted time frame of early developmental stages when MI oocytes undergo ICSI once completing maturation in vitro, even shortly after aspiration.