P-443 Evaluation of the effects of a semi-automated vitrification performed before or after in vitro maturation (IVM) on the kinetic of oocyte maturation and chromosome segregation
Authors: Marteil G , Chaput L , Dollet S , Pereira B , Eymard-Pierre E , Fiot M , Gouhier C , Grémeau A.S , Chauffour C , Tchirkov A , Brugnon F 
Published: June 2022

Abstract

Study question
What are the optimal vitrification method (semi-automated vs. manual) and oocyte stage for in vitro -matured oocyte cryopreservation using meiosis kinetics and chromosome segregation as readouts?

Summary answer
The semi-automated vitrification method does not impact oocyte nuclear maturation quality compared with the manual method. Immature oocyte cryopreservation should be performed after IVM.

What is known already
Fertility preservation using oocyte vitrification should be performed before oncological treatments. The reference protocol consists in collecting mature oocytes after ovarian stimulation. Nevertheless, ovarian stimulation sometimes yields immature oocytes or cannot be performed (e.g., emergency oncological treatment). An IVM step is therefore required but it is not clearly demonstrated whether IVM should be performed before or after vitrification. Oocyte vitrification is usually performed with manual methods. A semi-automated vitrification device (Gavi®, Genea Biomedx) showing high performances for embryo was recently released. To our knowledge, no study has analysed its efficiency on oocyte vitrification.

Study design, size, duration
200 immature oocytes collected from ICSI cycles from January 2020 will be used. Oocytes will be divided in five groups (40 oocytes/group): freshly matured oocytes (group 1 control), oocytes vitrified after IVM by a manual technique (group 2a) or by Gavi® (group 2b) and oocytes vitrified prior IVM (groups 3a and 3b). We assess oocyte nuclear maturation quality by evaluating IVM kinetics by time-lapse (Geri®) and the accuracy of homologous chromosomes segregation by CGH array.

Participants/materials, setting, methods
Since January 2020, 124 out of 200 immature oocytes have been included for this study. These oocytes provide from women under 37 years old without ovulatory disorder after signing an informed consent. The kinetics of meiotic resumption (germinal vesicle breakdown (GVBD) and polar body extrusion (PBE) timings), is determined by time-lapse technology (Geri®, Genea Biomedx). The accuracy of the homologous chromosome segregation during the first meiotic division will be assessed by CGH-Array.

Main results and the role of chance
The clinico-biological characteristics (age, BMI, smoking and total FSH dose) are comparable between the five groups (p &gt; 0.05). No significant difference in post-thawing oocyte survival rate is observed between the two vitrification methods (semi-automated 58% vs. manual 64%). A significant difference in the overall oocyte survival rate is observed according to the stage of vitrification with a significantly higher survival rate if oocytes are vitrified at the mature stage (93% (2a+2b) vs. 61% (3a+3b), p = 0.02). The IVM rate is significantly higher if oocytes are matured freshly (86% in group 1 (fresh IVM, n = 7) and 93% in group 2a+2b (IVM before vitrification, n = 27)) compared to post vitrification (71% in group 3a+3b, n = 28), p = 0.03. The vitrification technique does not seem to impact IVM rate since it reached 64% (group 3a, n = 11) and 76% (group 3b, n = 16) (p = 0.4). GVBD and PBE timings are not significantly different between the 5 groups, suggesting that neither the oocyte stage of vitrification nor the vitrification technique affects maturation kinetics. Similarly, our preliminary results of polar bodies and oocytes chromosomal profiles assessed by CGH-Array demonstrate a similar rate of aneuploidy (monosomy or trisomy) between the groups.

Limitations, reasons for caution
Our preliminary results of CGH array should be confirmed with the analysis of a larger number of IVM oocytes.

Wider implications of the findings
Vitrification of immature oocytes should be performed by semi-automated or manual methods after IVM. Tour knowledge, this is the first study comparing the efficiency of both semi-automated and manual vitrification methods on immature and in vitro-matured oocytes.

Trial registration number
NCT03680937