Effect of constant (5%) versus gradient (8%-2%) oxygen concentration on sibling human blastocyst development

Area of Science:

• Reproductive biology
• Embryology
• In vitro fertilization

Background:

• Optimizing oxygen concentration is crucial for human embryo development in vitro.
• Previous studies suggest varying oxygen levels may impact blastocyst formation.

Purpose of the Study:

• To compare the efficacy of a dynamic oxygen gradient versus static oxygen for human embryo culture.
• To determine if a stepwise reduction in oxygen concentration improves blastocyst development and morphology.

Main Methods:

• A prospective sibling-split study involving 658 oocytes from 44 intracytoplasmic sperm injection (ICSI) cycles.
• Embryos were alternately assigned to static 5% oxygen (control) or a dynamic gradient (8% to 2% oxygen).
• Time-lapse imaging and morphometric analysis were used to assess embryo development and blastocyst quality.

Main Results:

• The static 5% oxygen group yielded a significantly higher proportion of clinically usable blastocysts (47.3% vs. 36.9%).
• Rates of morphologically optimal day-5 blastocysts were comparable between groups.
• Dynamic oxygen culture led to delayed blastulation, expansion, and smaller blastocyst size.

Conclusions:

• Gradually decreasing oxygen concentration during the second half of embryo culture is detrimental to blastocyst development.
• Static 5% oxygen culture is more effective for producing clinically usable blastocysts.
• Dynamic oxygen gradients may negatively impact key developmental milestones in human embryos.