Embryo Developmental Potential in a Novel 2-step IVM System

Overview

In vitro maturation is a valid option for PCO(S) patients in the daily ART clinic, however maturation and embryologic development are not yet matching the efficiency levels obtained by standard COS treatment. To further enhance embryo quality after IVM, it was hypothesized to keep the connection and communication between oocyte and cumulus cells intact for a prolonged pre-maturation culture before IVM was initiated. This has been investigated and established using a meiotic blocker C-type Natriuretic peptide (CNP). The CNP peptide is present in high concentrations in the growing follicle, is produced by the mural granulosa cell compartment and binds to the Natriuretic peptide receptor 2 (NRP2) present in the cumulus cells. Binding of CNP on NRP2 leads to intracellular cGMP increase in cumulus cells, which travels through the transzonal projections to the oocyte. In the oocyte, cGMP will block the resumption of meiosis. Using CNP as natural inhibitor of meiosis, a new medium was designed to allow oocyte and surrounding cumulus cells to communicate and hence gain in competence for an additional culture period: the pre-maturation phase or Capacitation phase (CAPA). This system was devel-oped in mouse, tested in human in UZ Brussel on research material (toelating federaal EC: CFE-FCE ADV\_073\_ZUBrussel, toelating lokaal EC: 2016/411 BUN 143201630723) and used in a clinical setting in Vietnam.

The current IVM system in use in the clinic has a single step approach and seems to be less efficient compared to research and literature findings using a biphasic CAPA-IVM system in terms of maturation. To ascertain the efficiency of the biphasic CAPA-IVM system, both standard IVM and CAPA-IVM will be performed on sibling oocytes: maturation in standard IVM in the investigator's center is on average 47.5%, where CAPA-IVM reaches 62% maturation in literature. The investigators aim to prove superiority of the CAPA-IVM system in terms of maturation. Also fertilization and embryo development will be compared. The participants admitted to the study will be receiving both the standard IVM treatment for part of the participant's oocytes and the biphasic CAPA IVM system for the second part of the participant's oocytes. In one ovary a regular oocyte pick up (OPU) will take place with oocytes assigned to the standard IVM treatment, in the other ovary the CAPA IVM system will be applied. This means oocytes that are liberated from the follicular environment need to be exposed immediately to the inhibiting CNP peptide and herefore the tubes to collect the follicle fluid from the punctured follicles are prefilled with CNP supplemented medium. The OPU procedure is identical for both ovaries and according to our standard OPU IVM procedure with the sole difference of empty or prefilled tubes to collect follicle fluid. Oocytes from the 2 ovaries are separately processed in the lab according to attributed protocol. After IVM of oocytes, mature oocytes are subjected to ICSI with partner's sperm or donor sperm. Partner's sperm sample will be frozen at the latest the day of egg retrieval and will be thawed the day of intracytoplasmic sperm injection (ICSI): due to the use of 2 different IVM protocols with 2 different time lines (30 hours maturation versus 24 hours+30 hours maturation), ICSI will take place on two consecutive days with a freshly thawed straw of sperm cells for each day. Embryo development is followed until day 3 (cleavage stage) after ICSI. All embryos of sufficient quality will be vitrified for a deferred embryo transfer in a hormone replacement therapy (HRT) cycle. One embryo will be selected for embryo transfer based on the morphological quality assessment parameters, with the better quality as first choice for transfer, regardless the preceding IVM method. Frozen single embryo transfer cycles are repeated until pregnancy.