P-274 Humid or dry culture with medium renewal: impact on A-Grade Day 5 blastocysts. Randomized prospective cohort study
Authors: Mauri López A , Güell Penas E , Perulli Espino E  M , Cabré Fàbregas A , Mazzanti Pérez J  I 
Published: July 2024

Abstract

Study question
Could the humid embryo culture impact the development of top-graded blastocysts?

Summary answer
While no differences were observed in the overall blastocyst development rate, humidity conditions emerged as a significant factor influencing the achievement of A-Grade D + 5 blastocysts.

What is known already
In recent years, several publications have highlighted the advantages of humid culture (HC) over dry culture (DC) (&lt;45% relative humidity, RH). HC, with its lower risk of media evaporation and consequent osmolality changes. Nevertheless, to the best of our knowledge, this is the first prospective study addressing this aspect through oocytes from the same cohort.

Study design, size, duration
We have been conducting a randomized control trial (RCT) consisting on 379 MII oocytes from 30 patients from August 2022 until January 2024 (and ongoing). After ICSI procedure, sibling oocytes were divided following 1:1 ratio into both humid (&gt;70% HR) and dry (0% HR) chambers of a Geri incubator (Genea Biomedx, Australia). Ejaculated sperm ICSI cycles with &gt;5 fresh MII were included in the analysis. Time-lapse cleavage timings were manually gathered.

Participants/materials, setting, methods
Extended culture to the blastocyst stage (D + 5, D + 6 or D + 7) was performed in 80μL of single step G-TL medium (Vitrolife, Sweden). HC remained undisturbed while medium was renewed on D + 3 in DC by changing the culture dish. Fertilization, overall blastocyst development and A-Grade Day 5 blastocysts rates (ASEBIR’s morphology criteria) were compared. Statistical analysis consisted on Chi-squared test, t-student test and logistic regression for computation of Odds Ratio (OR, 95%CI).

Main results and the role of chance
While no statistically significant differences were observed in the fertilization rate (DC: 76.4%; HC: 69.1%, NS) or the overall usable blastocyst development rate (DC: 48.6%; HC: 53.1%, NS), noteworthy distinctions emerged in the proportion of top-graded embryos based on ASEBIR’s morphology criteria. Specifically, the A-Grade Day 5 blastocyst development rate displayed significant disparities when comparing all fertilized embryos in each culture type (DC: 19.9%; HC: 32.3%; p &lt; 0.05) and also among all usable blastocysts (DC: 40.8%; HC: 60.9%, p &lt; 0,05). The Odds Ratio for achieving A-Grade Day blastocysts depending on type of humidity conditions was 1.87 (1,099 – 3,235) for the humid culture.
Moreover, time-lapse imaging facilitated the detection of direct cleavage presence, which was similarly distributed between both incubation types (DC: 27/146; HC: 23/130, NS). However, only 3 embryos showing direct cleavage and cultured in HC reached the blastocyst stage at Day 6, while in dry incubator, 10 embryos with direct cleavage were able to develop to usable blastocysts, three of them being A-Grade on Day 5.

Limitations, reasons for caution
This study is currently ongoing, aiming to increase the sample size. Future analyses will explore clinical outcomes, especially for underrated embryos, day 6 blastocysts, and those with morphodynamic phenomena. While A-grade blastocyst rate variations may not impact pregnancy outcomes directly, they could influence cumulative success rates.

Wider implications of the findings
These data highlight that day+3 medium renewal doesn’t equalize conditions to humid culture. Ongoing efforts involve validating these insights through an expanded sample size and extensive outcome analysis. Investigating the long-term impact on clinical outcomes and refining culture protocols can amplify the relevance of these findings in assisted reproductive technologies.

Trial registration number
pending_protocolOK