Impact of 3.5% O2 culture on embryo development and clinical outcomes: a comparative study

Using 3.5% O2 concentration improves fertilization rates but decreases blastocyst formation and clinical pregnancy rates in intracytoplasmic sperm injection cycles.

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Volume 108, Issue 4, Pages 635–641


Mohamed Fawzy, M.D., Mai Emad, B.Sc., Mohamed Y. AbdelRahman, M.D., Hazem Abdelghafar, M.D., Faten F. Abdel Hafez, M.D., Mohamed A. Bedaiwy, M.D., Ph.D.



To evaluate the effect of culturing human embryos in vitro in 3.5% oxygen (O2) concentration.


Comparative study.


Private IVF center.


The study included 558 women in two groups.


After intracytoplasmic sperm injection (ICSI), women's oocytes were assigned to undergo cultivation in either 3.5% O2 concentration (intervention) or 5% O2 level (control group), continuously, from day 0 through day 5 or 6.

Main Outcome Measure(s)

Clinical pregnancy rate (PR) after ET.


There were significantly higher fertilization and cleavage rates in the 3.5% O2 group (odds ratio [OR] 1.72, 95% confidence interval [CI] 1.53–1.93) and (OR 3.74, 95% CI 2.30–6.07) than in the 5% O2 group. The compaction rate on day 3, and the number of formed, high-quality and cryopreserved blastocysts on day 5 were significantly lower in 3.5% O2 than in 5% O2 concentration ([OR 0.81, 95% CI 0.69–0.91], [OR 0.40, 95% CI 0.36–0.46], [OR 0.32, 95% CI 0.28–0.37] and [OR 0.47, 95% CI 0.40–0.54]), respectively. Culturing embryos in 3.5% O2concentration led to significantly lower rates of biochemical pregnancy, clinical PR, and implantation ([OR 0.66, 95% CI 0.47–0.92], [OR 0.60, 95% CI 0.43–0.84] and [OR 0.61, 95% CI 0.46–0.81]), respectively.


Culturing human embryos, continuously from day 0 to 5 or 6, in 3.5% O2 concentration is associated with significantly lower blastocyst formation rate and clinical outcomes parameters, but rather with significantly higher rates of fertilization and cleavage. Whether these findings hold true for other patient populations and culture media brands remain unknown.

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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility® is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders.