Expert's Perspective

Improving IVF Success Rates: Using Low Oxygen in the Lab

Paramount to the success of an IVF cycle is the IVF laboratory handling the gametes and embryos. While an IVF laboratory can’t turn a poor quality egg or sperm into a good quality embryo (at least not yet), they certainly can create conditions that result in a good egg or sperm yielding a poor quality embryo. Thus, when looking at IVF programs, select a program that has a cutting edge laboratory using optimal conditions to foster embryo growth.

Like many things in life, there is more than one way to accomplish the same endpoint within an IVF lab. However, there are a few key “best practices” for successful embryo growth, and use of low oxygen levels in the incubator is clearly one.

In the modern embryo culture system, use of low oxygen is essential. Culturing embryos in reduced oxygen concentrations (~5%), compared to atmospheric concentrations of ~21%, has long been recognized as superior in various animal IVF systems [1-7]. This makes sense when one considers the female reproductive tract appears to have oxygen levels between 2-8% (see reviews [5, 8]). Numerous studies have also demonstrated improved human embryo development, implantation, and pregnancy rates when using reduced oxygen concentrations [9-21]. Admittedly, confounding variables in some studies can make direct comparisons difficult. However, it is difficult to identify a study that demonstrates a detriment to using low oxygen for growing embryos. Importantly, use of low oxygen throughout the entire culture period of 5-6 days appears to be required to see the most benefit [9, 11, 12].

One of the better designed studies — a prospective randomized controlled trial at a high-performing program — showed that use of low oxygen significantly improved pregnancy, implantation and live birth rates [11]. Embryos cultured under low oxygen resulted in almost a 15% increase in live birth. Similar improvements of ~10-18% in live birth have been reported by others using low oxygen [12,22] and confirmed via a Cochrane review and meta-analysis [23, 24].

This is important to know because not all IVF labs have the capability to use low oxygen culture. This requires specialized incubators and or gas supply. In a web-based survey of embryologists, it was noted that more than 31% of IVF labs in North America were not using low oxygen culture conditions in their incubators to grow embryos [25]. This means you have approximately a 1 in 3 chance of selecting an IVF clinic that is not using the optimal low oxygen culture conditions. Only ~24% of labs surveyed were using low oxygen conditions exclusively.

So, when looking for an IVF center, in addition to looking at success rates and ensuring you’ll like the physician/nurses, make sure to ask about growth conditions used in the lab as well.

  1. Lonergan, P., et al., Oocyte and embryo quality: effect of origin, culture conditions and gene expression patterns. Reprod Domest Anim, 2003. 38(4): p. 259-67.
  2. Kelley, R.L. and D.K. Gardner, Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro. Reprod Biomed Online, 2016.
  3. Preis, K.A., G.E. Seidel, Jr., and D.K. Gardner, Reduced oxygen concentration improves the developmental competence of mouse oocytes following in vitro maturation. Mol Reprod Dev, 2007. 74(7): p. 893-903.
  4. Thompson, J.G., et al., Effect of oxygen concentration on in-vitro development of preimplantation sheep and cattle embryos. J Reprod Fertil, 1990. 89(2): p. 573-8.
  5. Wale, P.L. and D.K. Gardner, The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction. Hum Reprod Update, 2016. 22(1): p. 2-22.
  6. Lonergan, P., M. O'Kearney-Flynn, and M.P. Boland, Effect of protein supplementation and presence of an antioxidant on the development of bovine zygotes in synthetic oviduct fluid medium under high or low oxygen tension. Theriogenology, 1999. 51(8): p. 1565-76.
  7. Tervit, H.R., D.G. Whittingham, and L.E. Rowson, Successful culture in vitro of sheep and cattle ova. J Reprod Fertil, 1972. 30(3): p. 493-7.
  8. Gardner, D.K., The impact of physiological oxygen during culture, and vitrification for cryopreservation, on the outcome of extended culture in human IVF. Reprod Biomed Online, 2016. 32(2): p. 137-41.
  9. Kovacic, B. and V. Vlaisavljevic, Influence of atmospheric versus reduced oxygen concentration on development of human blastocysts in vitro: a prospective study on sibling oocytes. Reprod Biomed Online, 2008. 17(2): p. 229-36.
  10. Kovacic, B., M.C. Sajko, and V. Vlaisavljevic, A prospective, randomized trial on the effect of atmospheric versus reduced oxygen concentration on the outcome of intracytoplasmic sperm injection cycles. Fertil Steril, 2010. 94(2): p. 511-9.
  11. Meintjes, M., et al., A controlled randomized trial evaluating the effect of lowered incubator oxygen tension on live births in a predominantly blastocyst transfer program. Hum Reprod, 2009. 24(2): p. 300-7.
  12. Waldenstrom, U., et al., Low-oxygen compared with high-oxygen atmosphere in blastocyst culture, a prospective randomized study. Fertil Steril, 2009. 91(6): p. 2461-5.
  13. Kea, B., et al., Effect of reduced oxygen concentrations on the outcome of in vitro fertilization. Fertil Steril, 2007. 87(1): p. 213-6.
  14. Dumoulin, J.C., et al., Effect of oxygen concentration on human in-vitro fertilization and embryo culture. Hum Reprod, 1999. 14(2): p. 465-9.
  15. Catt, J.W. and M. Henman, Toxic effects of oxygen on human embryo development. Hum Reprod, 2000. 15 Suppl 2: p. 199-206.
  16. Ciray, H.N., et al., In vitro culture under physiologic oxygen concentration improves blastocyst yield and quality: a prospective randomized survey on sibling oocytes. Fertil Steril, 2009. 91(4 Suppl): p. 1459-61.
  17. Bahceci, M., et al., Effect of oxygen concentration during the incubation of embryos of women undergoing ICSI and embryo transfer: a prospective randomized study. Reprod Biomed Online, 2005. 11(4): p. 438-43.
  18. Nanassy, L., et al., Comparison of 5% and ambient oxygen during days 3-5 of in vitro culture of human embryos. Fertil Steril, 2010. 93(2): p. 579-85.
  19. Gomes Sobrinho, D.B., et al., IVF/ICSI outcomes after culture of human embryos at low oxygen tension: a meta-analysis. Reprod Biol Endocrinol, 2011. 9: p. 143.
  20. Petersen, A., A.L. Mikkelsen, and S. Lindenberg, The impact of oxygen tension on developmental competence of post-thaw human embryos. Acta Obstet Gynecol Scand, 2005. 84(12): p. 1181-4.
  21. Bedaiwy, M.A., et al., Relationship of reactive oxygen species levels in day 3 culture media to the outcome of in vitro fertilization/intracytoplasmic sperm injection cycles. Fertil Steril, 2010. 94(6): p. 2037-42.
  22. Kasterstein, E., et al., The effect of two distinct levels of oxygen concentration on embryo development in a sibling oocyte study. J Assist Reprod Genet, 2013. 30(8): p. 1073-9.
  23. Bontekoe, S., et al., Low oxygen concentrations for embryo culture in assisted reproductive technologies. Cochrane Database Syst Rev, 2012. 7: p. CD008950.
  24. Mantikou, E., et al., Low oxygen concentrations for embryo culture in assisted reproductive technologies. Hum Reprod Update, 2013. 19(3): p. 209.
  25. Christianson, M.S., et al., Embryo catheter loading and embryo culture techniques: results of a worldwide Web-based survey. J Assist Reprod Genet, 2014. 31(8): p. 1029-36.
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