P-224 The sex of the human embryos affects the oxidation profile of the spent culture media
Authors: Viloria Samochin T.A , Valera M.Á , Garg A , Bori L , Romany L , Aparicio-Ruiz B , Meseguer M 
Published: June 2022

Abstract

Study question
Is the oxidative status of the spent culture media used in ICSI treatments related to embryo sex and newborn characteristics?

Summary answer
Female embryos produce higher levels of oxidative stress in the culture media than male embryos.

What is known already
Sex-associated differences in embryo development have previously been observed. Studies suggest that male embryos have a faster pre-implantation development, higher morphological grading and lower glucose consumption (Nasiri et al, 2018). The thermochemiluminiscence (TCL) assay quantifies the oxidative status of biological samples by catalyzing an oxidative reaction through heating and counting the photons emitted per second. TCL parameters are directly correlated to the content of oxidant agents in the sample. Previous analysis used TCL assay to relate higher oxidative metabolism in embryos with higher viability. Analysis of spent culture media with TCL could be a potential biomarker for embryo sex prediction.

Study design, size, duration
Prospective observational study over 86 transferred blastocysts (all single embryo transfer) that reached life-birth, belonging to ICSI treatments, including autologous and oocyte donation, performed in a single fertility clinic during three consecutive years. The oxidative status of the spent culture media was analyzed and compared with the characteristics of the newborns.

Participants/materials, setting, methods
Embryo cohorts were cultured in individual wells in an Embryoscope incubator, using single-step Gems culture media (Genea Biomedx). The best embryo of the cohort was selected for transfer using morphologic (ASEBIR) and morphokinetic criteria (KID Score algorithmTM, Vitrolife, (KS)). Spent culture media was analyzed in the Fertissimo TCL Analyzer (Carmel Diagnostics, Israel) and oxidation parameters were compared with the sex, weight and height of the newborns through ANOVA, C2 and Pearsons Correlation coefficient (PCC) tests.

Main results and the role of chance
The sex ratio of the embryos (male to female) resulted 59.3%. The sex ratio was increasingly higher the better morphological classification: C = 16.7%, B = 56.0%, A: 73.3%. KS did not give significantly different scores to the embryos depending on their sex: average KS (female)=6.78 vs average KS (male)=7.03, P = 0.621. No correlation was found between KS or the morphological classification and the weight and height of the babies: PCC (KS-height)=0.158, P = 0.349; PCC (KS-weight)=0.082, P = 0.569; average newborn height: C = 51.67±1.15cm, B = 50.57±3.48cm, A = 50.92±1.95cm, P = 0.791, average newborn weight: C = 3,386.00±459.11g, B = 3,283.35±658.12g, A = 3,229.07±732.13g, P = 0.877. TCL ratio (slope of the time curve of photon emission, representing the level of oxidant agents in the sample) was statistically significantly higher in the culture media of female embryos than of male embryos: Ratio (female)=119.54±13.37 vs Ratio (male)=111.62±15.80, P = 0.017. No statistically significant difference was found in the TCL Ratio between the three morphological classes, although the tendency of the data is towards lower levels with increasing morphological classification: Ratio (C)=120.40±14.43, ratio (B)=116.32±14.39 and ratio (A)=111.27±16.62, P = 0.237. No correlation was found between the TCL parameters and the weight and height of the newborn: PCC (Ratio-height)=-0.173, P = 0.198; PCC (Ratio-weight) 0.036, P = 0.753.

Limitations, reasons for caution
Patient demographics, habits and male sperm characteristics were not considered for the analysis, but might impact embryo characteristics and intrauterine development of the fetus. A larger scale study should be performed to validate results.

Wider implications of the findings
The differential oxidative load embryos exert over the culture medium might be related to a glucose consumption-associated sex dimorphism. Measuring the oxidative status of the culture medium could serve as a non-invasive biomarker for embryo sex selection. This technique could be an interesting option in carriers of sex-linked diseases.

Trial registration number
not applicable