P–269 Effect of well-of-the-well culture as in vitro maturation system for human oocytes

Study question

Can the Well-of-the-Well system (WOW), applied on denuded oocytes, improve germinal vesicle breakdown (GVBD) and maturation rate?

Summary answer

In vitro maturation (IVM) of denuded germinal vesicle (GV) oocyte using WOW culture system increases nuclear maturation competence when compared with droplet conventional culture

What is known already

Further research remains necessary to address the mechanism of oocyte maturation in order to refine culture conditions and improve the implantation rate of in vitro matured oocytes. Several studies on bovine oocytes have shown that oocyte-secreted factors (an uncharacterized mix of growth factors secreted by the oocyte) enhance oocyte developmental competence during in vitro maturation. These oocyte-secreted factors may accumulate at the bottom of the micro-well, as suggested for the WOW culture system. Previous reports suggested that diffusible factors secreted by individual oocytes probably accumulated in a micro-well WOW dish, may provide a suitable microenvironment for their in vitro maturation.

Study design, size, duration

A total of 879 GV collected between 2017 and 2019 were included in this study. They were randomly allocated into two experimental groups: (1) single-cultured oocytes (SC) that were cultured individually in micro-droplets, and (2) group-cultured oocytes (WOW) that were cultured in a microwell culture system using the WOW dish (culture dish for time lapse incubator). The nuclear maturation was assessed after 24 hours and 48 hours of IVM

Participants/materials, setting, methods

GV oocytes were obtained from 609 patients undergoing controlled ovarian stimulation cycles. Oocytes from the experimental group (1) were placed individually in conventional 25μl micro-droplets in a 35 mm dish. Oocytes from the experimental group (2) were placed in 80 μl droplet individually in each of 9 microwells of WOW dish. All GV oocytes were matured in a single step embryo culture medium, supplemented with human menopausal gonadotropin and synthetic serum substitute.

Main results and the role of chance

Mature oocyte (MII) was considered when we observed rupture of the GV and the presence of a first polar body in the perivitelline space during the first 24 or 48 hours of culture under inverted optical microscope. GVBD noted significant differences (p-valor = 0.000) between the study groups after culturing of 24 hours [GVBD: SC group; 70% (318/455) vs. WOW group; 83% (352/424)] and 48 hours [GVBD: SC group; 77% (319/416) vs. WOW group; 94% (398/424)]. The maturation rates (MR) showed significant differences (p-valor = 0.000) between the study groups after culturing of 24 hours [MR: SC group; 51% (233/455) vs. WOW group; 80% (338/424)] and 48 hours [MR: SC group; 71% (295/416) vs. WOW group; 91% (387/424)].

Limitations, reasons for caution

There is no data on cleavage and blastocyst rates.

There are no previous reports comparing the maturation rates in denuded human oocytes single-cultured in individually droplet or group-cultured in WOW dish.

Wider implications of the findings: Our results must be taken into account in order to improve the culture conditions for the optimization of the in vitro maturation technique in human oocytes from stimulated cycles.

We now provide evidence that group-cultured oocytes in WOW dish increase GVBD and maturation rates.

Trial registration number

Not applicable