P-237 In vitro time to maturation of Metaphase I oocytes: a time-lapse study correlating blastocyst formation and ploidy status
Authors: Erberelli R , Nicolielo Barreto M , Aiello B , Motta E L A , Chehin M B , Alegretti J R , Lorenzon A 
Published: June 2023

Abstract

Study question
What is the impact of metaphase I (MI) time to mature period (TTM) regarding blastocyst development and ploidy status?

Summary answer
A short period of TTM (0.1 to 1.0) is related to an increase number of blastocyst formation when compared to longer TTM (1.1 to 3.0).

What is known already
To achieve meiotic competence, coordinated nuclear and cytoplasmic changes must occur in the oocyte to support fertilization and DNA replication and to ensure correct ploidy of the zygote and embryonic genome activation. Concomitant with chromosome condensation and migration, oocyte maturation goes by cytoplasm reorganization throughout the transitions of MI, polar body extrusion and MII. Despite the optimization of COH protocols, nearly 20% of the retrieved oocytes remain immature at the GV or MI stages. In vitro maturation of MI could increase the number of available embryos; however, longer culture time may affect oocyte quality, resulting in abnormal fertilization and cleavage.

Study design, size, duration
Prospective cohort study from 244 patients (n = 277 cycles) that had at least 1 MI oocyte after oocyte retrieval (OPU) following controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF) treatment according to medical referral in an single private ART center from January/2019 to November/2022. All MI oocytes were placed in a time-lapse incubator (TL, EmbryoScope, Vitrolife, Sweden) to check the exact time of first polar body extrusion (TTM to MII) before intracytoplasmic sperm injection (ICSI).

Participants/materials, setting, methods
Three hours after OPU, oocytes were denuded and assessed for maturation. Six-hundred and seven MI oocytes were followed in TL and those that reached the MII stage in a maximum of 6 hours post-OPU, were injected by ICSI (at 6h post-OPU) and stratified according to the TTM (0.1-1.0 hours and 1.1-3.0 hours). Fertilization rate, blastocyst formation, and ploidy were assessed. Kruskal-Wallis, chi-squared and Fisher tests were applied for statistical analysis. p &lt; 0,05 was considered significant.

Main results and the role of chance
Patient mean age (n = 244) was 38,50 ± 3,40 years. From those, 25 patients (10.3%) had 2 cycles and 4 patients (1.6%) had 3 cycles with at least 1 MI oocyte. Age, anti-Müllerian hormone (AMH), #OPU, #MII, %MII (MII/OPU), #MI and MI% (MI/OPU) mean were not statistically different in patients with 1, 2 or 3 cycles in our cohort. One hundred forty-nine patients (61%) in 165 cycles (59.6%) had at least 1 oocyte that reached MII stage. In total, 248 oocytes were injected after 0.1-1.0h (group 1, n = 104, 41.9%) and 1.1-3.0h (group 2, n = 144 oocytes, 58.1%) of in vitro maturation. Age (38,99 ± 3,01 vs 38,85 ± 3,31), AMH (1,27 ± 1,29 vs 1,63 ± 1,87), #OPU (8,98 ± 4,32 vs 8,90 ± 4,34), #MII (4,41 ± 2,74 vs 4,44 ± 2,178), %MII (47.6% ± 18.8% vs 48.4% ± 17.1%) and %MI that followed to ICSI (59.2% ± 28.5% vs 54.8% ± 29.2%) were not different between groups 1 and 2 respectively. The mean number of MI that followed to ICSI were higher in group 1 (1,28 ± 0,48 vs 1,10 ± 0,32, p = 0.0008). Normal fertilization (2PN) and embryo cleavage were similar between groups (54.8% vs 45.1%, p = 0.157, 96.6% vs 93.3%, p = 0.467, respectively). However, blastocyst formation rate (#blastocyst/#fertilized) was higher in group 1 (n = 33, 55.9% vs n = 26, 34.7%, p = 0.015). Euploidy rates were similar between groups (9/28, 32% vs 4/24, 16%, p = 0.336).

Limitations, reasons for caution
Besides the retrospective nature of this study, male factor and infertility reason were not considered in this analysis. Due to the low number of blastocyst formation and consequentially ploidy assessment and number of embryo transfer, the results regarding euploidy rate may be underestimated and pregnancy rates were not included.

Wider implications of the findings
Oocytes that reached maturity up to 1 hour after denudation showed higher blastocyst formation rate, thus increasing embryo availability to transfer. In vitro-matured oocytes exhibit increased spindle and chromosomal abnormalities compared with oocytes matured in vivo, which may explain the lower rates of euploid embryos, especially in group 2.

Trial registration number
Not applicable.