P-148 Humid versus dry culture: impact on euploidy, live birth sex ratio and clinical outcomes
Authors: Serrano-Novillo C , Pons S , Fusté A , Marquez Guevara C 
Published: July 2024

Abstract

Study question
Does humidity have an impact on top-quality blastocyst rate, ploidy, live birth sex ratio and clinical outcomes?

Summary answer
Humid culture conditions in time-lapse incubators may enhance clinical outcomes, particularly in autologous cycles, without biasing euploidy or newborn sex.

What is known already
Recent advances in assisted reproductive technology have focused on improving embryo culture conditions and incubators are becoming more sophisticated. Although culture conditions such as oxygen and temperature are well-studied, the optimal humidity level remains uncertain. Dry atmospheres favour higher evaporation of culture media compared to humid conditions, increasing its osmolality. This appears to be detrimental to several animal model embryos: developmental arrest, changes in gene expression and epigenetic alterations in the embryos. Previous studies have shown than incubator humidification improves clinical outcomes and embryonic development. However, other studies showed no significant improvements.

Study design, size, duration
A single center retrospective study was performed. Data included a total of 793 cycles of IVF/ICSI between January 2019 and May 2023.

Participants/materials, setting, methods
793 cycles of IVF/ICSI from 734 patients were studied. Study population was categorized in autologous (n = 544) and egg-donation (n = 249) cycles. A total of 5909 embryos were included in the study. Patients were randomly distributed in two distinct cohorts at the moment of their treatment: dry condition (DC) and humid condition (HC). Blastocyst quality (BR), biochemical pregnancy (BPR), implantation rate (IR), live birth rate (LBR) were studied. Ploidy rate and LB sex ratio was also studied.

Main results and the role of chance
In egg donation cycles, no differences were observed between HC and DC groups in the rates of top-quality blastocysts (61.5 HC vs 64.4% DC), BPR, (71.1% HC vs 71.2% DC), IR (53.8% HC vs. 59.2% DC) or LBR (51.9% HC vs. 44.8% DC). However, autologous cycles showed an improvement when humid conditions were used. BR and IR were higher in humid conditions (BR: 58.8% HC vs. 55,6% DC, p-value 0.03; IR:57.1% HC vs. 39.7% DC, p-value 0.011)). Humid and dry culture conditions yielded similar rates of BPR (65.0% HC vs 53.0% DC, p-value: 0.11) and live birth rate (44.3% HC vs 34.5% DC, p-value: 0.16). Although there is a tendency towards a 20% of benefit in presence of humidity in both rates, no significance was reached.
No differences were found in euploidy between dry and humid groups. When stratifying patients by age, all age groups met the ploidy expected rates in both culture conditions.
Humid culture conditions enhance clinical outcomes, particularly in autologous cycles. Donated oocytes may take advantage of their better quality to compensate the detrimental effect of dry ambients. Our study, moreover, demonstrates that humidity does not introduce any bias towards chromosomal alterations or newborn sex.

Limitations, reasons for caution
This is a retrospective study and should be further confirmed with a prospective randomized study. Sample size should be increased, especially for ploidy Specific humidity values could also be tested.

Wider implications of the findings
Humid culture conditions may highly improve ART outcomes for particular groups of patients. If tested with stratified groups by age, a specific age group might be especially benefited of humidity, without any bias in sex ratios when best embryo is transferred in fresh cycles.

Trial registration number
not applicable