P-251 Denudation time is crucial to increase the proportion of top-quality embryos in egg donation cycles
Authors: Martiñá Rivas L , Rovira Fontanals S , Rovira Ripoll M , Acín Vinyeta L , De Rocco M , Moffa F , Antich Díaz M , Novo Bruña S 
Published: July 2024

Abstract

Study question
How do different denudation times affect in the efficiency of the egg donation cycles?

Summary answer
Undetected in vitro matured oocytes, resulting from delayed denudations, contribute to a decreased top-quality blastocyst ratio.

What is known already
While the timeframe for sperm microinjection in ICSI cycles is widely agreed upon (2-6 hours post-oocyte retrieval), no definitive denudation time preference has been established. Published studies diverge on the advantages of early or late denudation, assessing the impact of trigger-to-denudation time (T-D time) on oocyte maturation. Advocates of early denudation contend it prevents oocyte aging, reducing in vitro culture and enhancing outcomes. These studies, often using data from cycles with own oocytes, exhibit high variability and inconsistent conclusions. The present work introduces an alternative hypothesis on the benefits of early denudation, employing a more stable study model.

Study design, size, duration
This retrospective study encompasses oocyte donation cycles, employing a short antagonist protocol and ovum pick-up 35.5 hours post-trigger, conducted from January 2019 to July 2023 including 1,559 stimulations. Additionally, 1,275 ICSI cycles without detected sperm pathologies derived from these stimulations were examined to evaluate the influence of T-D time on the reproductive outcomes. Six comparable groups were established by segmenting the sample according to T-D time, annotated in 30-minute intervals (36.5h to 39h).

Participants/materials, setting, methods
Rates of MII, MI, and nonviable oocytes were examined among 1,559 stimulations resulting in 29,671 oocytes (36.5h:187-stimulations/3,178-oocytes; 37h:226/3,836; 37.5h:614/11,921; 38h:329/6,884; 38.5h:119/2,322; 39h:84/1,530). Additionally, in 1,275 ICSI cycles involving 11,333 MII-oocytes (36.5h:117-ICSI cycles/1,027-MII; 37h:130/1,133; 37.5h:502/4,426; 38h:316/2,925; 38.5h:120/1,041; 39h:90/781), comparisons were made for fertilization, abnormal fertilization, ICSI degeneration, useful day 5/6 blastocyst (transferred or cryopreserved; &gt;3BB-top and ≤3BB-good quality by Gardner score), pregnancy, and live birth rates. Statistics were ANOVA, Chi-square test and Pearson’s correlation.

Main results and the role of chance
Oocyte maturation profile assessment reveals that groups with later denudation exhibit a higher proportion of MII-oocytes (36.5h:80.71%; 37h:81.04%; 37.5h:81.26%; 38h:80.83%; 38.5h:84.84%; 39h:85.29%; r:0.8475; p &lt; 0.05), reaching significance from 38.5h onward (p &lt; 0.05). This is complemented by a strong negative correlation between T-D time and MI rate (36.5h:5.51%; 37h:5.32%; 37.5h:4.64%; 38h:4.17%; 38.5%h:3.27%; 39h:2.94%; r:-0.9881; p &lt; 0.05), with significant declines at 38h and 38.5h (p &lt; 0.05). No correlation between useless oocytes proportion and T-D time was observed (r:-0.5983; p = 0.21). This illustrates that certain MI-collected oocytes progressively mature during in vitro culture and subsequently, upon denudation, are classified as MII. This overestimates in vivo-matured oocytes.
No differences attributed to T-D time were observed regarding fertilization, abnormal fertilization, or ICSI degeneration rates. While time does not affect the rate of useful embryos achieved (36.5h:49.4%; 37h:46.4%; 37.5h:44.6%; 38h:48.0%; 38.5h:50.6%; 39h:47.2%; r:0.1342; p = 0.80), it has an impact on the blastocysts quality. The proportion of top-quality blastocysts (&gt;BB) progressively decreases with T-D time (36.5h:86.2%; 37h:85.2%; 37.5h:85.4%; 38h:81.2%; 38,5h:80.5%; 39h:80.5%; r:-0.925; p &lt; 0.05).
Out of 1,794 single embryo transfers, 1,477 have conclusive outcome. No implication of T-D time was detected in pregnancy rate (36.5h:59.88%; 37h:64.07%; 37.5h:61.54%; 38h:65.02%; 38.5h:59.55%; 39h:62.26%; r:0.0489; p = 0.93) or live birth rate (36.5h:40.31%; 37h:51.85%; 37.5h:39.12%; 38h:45.04%; 38.5h:41.83%; 39h:37.96%; r:-0.375; p = 0.46).

Limitations, reasons for caution
This study has inherent limitations as a retrospective analysis. Additionally, the potential effects of a denudation earlier than 36.5 hours post-trigger, not yet standardized in the laboratory, were not assessed.

Wider implications of the findings
Delayed denudation may benefit autologous IVF by fostering in vitro oocyte maturation. In egg donation cycles, early denudation is preferable for stringent selection of in vivo matured oocytes, yielding superior results. Additionally, shortening or eliminating incubation periods would enhance the automated sequence of diverse processes during an IVF cycle.

Trial registration number
not applicable