The influence of oxygen concentration during embryo culture on obstetric and neonatal outcomes: a secondary analysis of a randomized controlled trial

Do IVF culture conditions have an impact on neonatal outcomes? A systematic review and meta-analysis

PURPOSE

Are embryo culture conditions, including type of incubator, oxygen tension, and culture media, associated with obstetric or neonatal complications following in vitro fertilization (IVF)?

METHODS

A systematic search of MEDLINE, EMBASE, and Cochrane Library was performed from January 01, 2008, until October 31, 2021. The studies reporting quantitative data on at least one of the primary outcomes (birthweight and preterm birth) for the exposure group and the control group were included. For oxygen tension, independent meta-analysis was performed using Review Manager, comparing hypoxia/normoxia. For culture media, a network meta-analysis was carried out using R software, allowing the inclusion of articles comparing two or more culture media.

RESULTS

After reviewing 182 records, 39 full-text articles were assessed for eligibility. A total of 28 studies were kept for review. Meta-analysis about the impact of incubator type on perinatal outcomes could not be carried out because of a limited number of studies. For oxygen tension, three studies were included. The pairwise meta-analysis comparing hypoxia/normoxia did not show any statistical difference for birthweight and gestational age at birth. For culture media, 18 studies were included. The network meta-analysis failed to reveal any significant impact of different culture media on birthweight or preterm birth.

CONCLUSION

No difference was observed for neonatal outcomes according to the embryo culture conditions evaluated in this review. Further research is needed about the safety of IVF culture conditions as far as future children's health is concerned.

Oxidative Stress in Pregnancy

Recent years have seen an increased interest in the role of oxidative stress (OS) in pregnancy. Pregnancy inherently heightens susceptibility to OS, a condition fueled by a systemic inflammatory response that culminates in an elevated presence of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the circulatory system. The amplified OS in pregnancy can trigger a series of detrimental outcomes such as underdevelopment, abnormal placental function, and a host of pregnancy complications, including pre-eclampsia, embryonic resorption, recurrent pregnancy loss, fetal developmental anomalies, intrauterine growth restriction, and, in extreme instances, fetal death. The body's response to mitigate the uncontrolled increase in RNS/ROS levels requires trace elements that take part in non-enzymatic and enzymatic defense processes, namely, copper (Cu), zinc (Zn), manganese (Mn), and selenium (Se). Determination of ROS concentrations poses a challenge due to their short half-lives, prompting the use of marker proteins, including malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), and glutathione (GSH). These markers, indicative of oxidative stress intensity, can offer indirect assessments of pregnancy complications. Given the limitations of conducting experimental studies on pregnant women, animal models serve as valuable substitutes for in-depth research. This review of such models delves into the mechanism of OS in pregnancy and underscores the pivotal role of OS markers in their evaluation.

Oxygen concentration from days 1 to 3 after insemination affects the embryo culture quality, cumulative live birth rate, and perinatal outcomes

PURPOSE

We aimed to compare embryo development, cumulative live birth rate (CLBR), and perinatal outcomes of embryos cultured in 20% and 5% oxygen from days 1 to 3 after insemination.

METHODS

This retrospective study included patients who received in vitro fertilization (IVF) treatment between January 2015 and November 2019. Embryos of each patient were cultured at 20% or 5% oxygen from days 1-3 after insemination. The primary outcome was CLBR. Propensity score matching (PSM) was used to balance patients' baseline data in both oxygen groups.

RESULTS

In total, 31,566 patients were enrolled. After PSM, the rate of high-quality day 3 embryos was significantly lower in the 20% than in the 5% oxygen group (0.49 ± 0.33 vs 0.51 ± 0.33; adjusted β = -0.03; 95% confidence interval [CI], -0.03 to -0.02). The CLBR was significantly lower in the 20% than in the 5% oxygen group (58.6% vs. 62.4%; adjusted odds ratio = 0.85; 95% CI, 0.81-0.90). The birthweight and Z score of singletons were significantly higher in the 20% than in the 5% oxygen group (birthweight: 3.30 ± 0.50 vs. 3.28 ± 0.48; adjusted β = 0.022; 95% CI, 0.004-0.040; Z score: 0.26 ± 1.04 vs. 0.22 ± 1.01; adjusted β = 0.037; 95% CI, 0.001-0.074).

CONCLUSION

Culturing embryos at atmospheric oxygen concentrations from days 1 to 3 compromises embryo quality, reduces CLBR, and affects birthweight. The 5% oxygen concentration is more suitable for embryo culture in IVF laboratories to achieve successful outcomes.

Endogenous hydrogen sulfide promotes human preimplantation embryonic development by regulating metabolism-related gene expression

Hydrogen sulfide (H₂S) as an endogenous gaseous signaling molecule had been proved to play a vital role in gametes physiology, covering meiosis, maturation and aging. However, little is known about H₂S involvement in embryonic development. The present study explored the positive effect of H₂S on human early embryonic development. Results validated that the two H₂S producing enzymes, CBS and CSE mRNA and proteins were identified in donated human cleavage and blastocyst-stage embryos. The l-cysteine incubation produced endogenous H₂S in human blastocysts. NaHS positively affected in vitro blastulation. Single-cell RNA-seq analysis identified 228 differentially expressed genes (DEGs) after NaHS treatment versus the control. The Gene Ontology (GO) enrichment analysis of DEGs showed that genes for protein modification and metabolism were significantly enriched in the NaHS treatment group. For the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, 2-oxocarboxylic acid metabolism, glycosaminoglycan biosynthesis-keratan sulfate, steroid biosynthesis, carbon metabolism, and biosynthesis of amino acids were significantly enriched. Six DEGs, including Neural EGFL like 1 (NELL1), aconitase 1 (ACO1), phosphoglycerate mutase 1 (PGAM1), TP53 induced glycolysis regulatory phosphatase (TIGAR), UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 2 (B3GNT2), and carbohydrate Sulfotransferase 4 (CHST4) were validate by real-time RT-PCR. These findings suggest that H₂S is a positive regulator of early embryonic development and may alter the transcription of embryonic genes for protein modification and metabolism in human embryos.