IVF > IVF Mail

Michael L. Reed said on 06 November 2008

"The question regarding the best oxygen concentration for human IVF has been approached, essentially, in two ways.

First, using atmospheric oxygen is easy, and there are pregnancies, therefore it is ok to use approximately 20 to 21% atmospheric oxygen. Second, using physiological oxygen is less easy, but it is logical to assume that lower oxygen would be better for the embryos, as in the tissues, the embryos are exposed to say, around 5% or so oxygen in the oviduct and perhaps a bit higher in the uterus.

As to what the best concentration of oxygen is, there are no studies in the human where defined oxygen concentration increments, e.g. in 1% intervals from 0 to atmospheric (or higher), have been studied. From an ethical standpoint, one could start at 5% and work up to atmospheric oxygen easily enough, but lower and higher end studies, that might not be easily approved in the human.

I've found two animal references, that did study increments of oxygen tension on development:

Cattle embryos were cultured using 2.5% to 20% oxygen, and 5 to 10% O2 yielded a higher proportion of morulae, with the best development at 5% O2. Additionally, mean cell numbers per blastocyst were higher under 5% O2, compared to 20% O2 or co-culture.
Takahashi et al 1996 J Vet Med Sci 58:897-902.

Rabbit embryos were cultured under conditions of 1% to 20% O2 (steps of 5%). 5% O2 was found optimal for the proportion of hatching blastocysts, and cell numbers per embryo. And, interestingly, the embryos grown in 1% O2 were not substantially different from those grown in 5% O2.
Li and Foote 1993 J Reprod Fertil 98:163-167.

There are a number of very recent papers that support the use of lower oxygen tension (5%O2) for human IVF, in particular with extended embryo culture to day five. And to me, more importantly, there are a number of animal papers that demonstrate that gene expression patterns can be altered by oxygen tension, and that reduced oxygen culture conditions yield patterns of expression more similar to that found with in vivo embryos.

Of course, we still need the CO2 until someone develops a culture medium that can replace, successfully, the majority (not all) of the bicarbonate with some other buffer, that can maintain embryo friendly pH.

Oocyte maturation, it appears that maturation/competency might be more successful at higher oxygen tensions until time for fertilization, and as for sperm, I'd love to hear from andrologists on that one, as I don't have too many sperm incubation papers where oxygen has been looked at, other than those talking in terms of ROS effects.

Mike"

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