P-242 ICSI, the sooner, the better
Authors: Peinado Adiego L , Rovira Fontanals S , Lolicato F , Rodriguez Isern A , Pérez-Alzueta A , Moffa F , Antich Díaz M , Novo Bruña S 
Published: July 2024

Abstract

Study question
What is the impact of different ICSI timing on the efficiency of egg reception cycles concerning both denudation and trigger events?

Summary answer
The interval between denudation and ICSI significantly compromises cycle efficiency, particularly blastocyst quality. Delayed ICSI impairs this impact relative to the trigger event.

What is known already
The established consensus on the optimal ICSI timeframe, spanning 2-6 hours post-oocyte retrieval, has been extensively documented. However, the acknowledged variability within this window has prompted a critical review. Recent studies highlight the need for a more nuanced understanding, suggesting that phenomena affecting ICSI outcomes can be better elucidated by adopting stable models such as oocyte reception cycles. By removing the oocyte factor, these models offer a more precise perspective, addressing the temporal intricacies integral to successful ICSI procedures. The present research underscores the imperative of refining the temporal dimension for optimal reproductive results.

Study design, size, duration
This retrospective study encompassed 1,275 egg reception ICSI-cycles conducted between January 2019 and July 2023. Donors underwent stimulation using a short antagonist protocol, and oocytes were collected 35.5h post-trigger. The impact of both, the time between denudation-ICSI (D-ICSI time) and the time between trigger-ICSI (T-ICSI time) on reproductive outcomes were analysed. Six comparable groups were established by 30-minute intervals, segmenting the sample based on D-ICSI time (0.5h to 3h) and T-ICSI time (38h to 40.5h).

Participants/materials, setting, methods
A total of 1,275 cycles, involving 11,333 MII-oocytes, were stratified based on D-ICSI time (0.5h:89-cycles/761-MII; 1h:128/1,186; 1.5h:269/2,385; 2h:270/2,415; 2.5h:340/3,064; 3h:179/1,522) and T-ICSI time (38h:183/1,631; 38.5h:131/1,158; 39h:246/2,205; 39.5h:219/1,952; 40h:173/1,534; 40.5h:323/2,853). Comparative analyses were conducted for fertilization, abnormal fertilization, ICSI degeneration, and useful day 5/6 blastocyst outcomes (transferred or cryopreserved; &gt;3BB-top and ≤3BB-good quality by Gardner score), as well as pregnancy and live birth rates (1,594 SET). Statistical methods employed included ANOVA, Chi-square tests, and Pearson’s correlation.

Main results and the role of chance
Several parameters showed stability across different time intervals of D-ICSI time: fertilization (0.5h:74.6%; 1h:72.6%; 1.5h:74.0%; 2h:75.9%; 2.5h:74.8%; 3h:74.4%; r = 0.3707; p = 0.469), blastocyst (0.5h:65.3%; 1h:62.6%; 1.5h:61.7%; 2h:60.1%; 2.5h:64.8%; 3h:63.8%; r= -0.068; p = 0.898), and live birth rates (0.5h:39.5%; 1h:35.9%; 1.5h:36.6%; 2h:40.2%; 2.5h:39.9%; 3h:39.7%; r = 0.474; p = 0.342). However, an extended interval significantly correlated with increased oocyte ICSI-degeneration (0.5h:5.5%; 1h:6.7%; 1.5h:6.7%; 2h:6.5%; 2.5h:7.4%; 3h:8.5%; r = 0.903; p &lt; 0.05) and a decreased proportion of top-quality blastocysts (0.5h:86.8%; 1h:89.2%; 1.5h:86.4; 2h:85.3%; 2.5h:81.2%; 3h:75.2%; r= -0.879; p &lt; 0.05). Extended culture of cumulus cell-free oocytes may promote oocyte aging and, consequently, compromise optimal development (consistent with findings in other studies).
In evaluating T-ICSI time, similar trends to those observed in D-ICSI time persist in fertilization (r = 0.275, p = 0.598), blastocyst (r = 0.233, p = 0.657), live birth (r = 0.516, p = 0.295), and ICSI-degeneration rates (r = 0.864, p &lt; 0.05). The negative correlation in the quality of generated useful blastocysts significantly intensifies (38h:90.6%; 38.5h:87.5%; 39h:84.7%; 39.5h:82.4%; 40h:80.1%; 40.5h:79.7%; r= -0.982, p &lt; 0.05). In a separate analysis, we observed that undetected in vitro matured oocytes, stemming from delayed denudations, lead to a reduction in the top-quality blastocyst ratio. This concept, along with D-ICSI time, seems to synergize, emphasizing the adverse trend when evaluating blastocyst qualities concerning T-ICSI times.

Limitations, reasons for caution
This study has inherent limitations as a retrospective analysis. Additionally, the potential effects of ICSI earlier than 0.5 hours post denudation and 38 hours post-trigger, not yet standardized in the laboratory, were not assessed.

Wider implications of the findings
Extended incubation of denuded and non-injected oocytes fosters oocyte aging. Consequently, cycle efficiency is compromised with prolonged incubation times. The reduction of these times holds promise for improving the efficiency of IVF treatments. Additionally, shortening or eliminating incubation periods would enhance the automated sequence of diverse processes during an IVF.

Trial registration number
not applicable