Low O2 Incubators
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In the IVF laboratory we strive to provide the very best conditions under which we can maintain sperm, eggs and embryos. Sperm are resilient and could tolerate a little hardship, but eggs and embryos are extremely sensitive to their environment. Sperm are quite happy at room temperature, for example, but eggs suffer irreversible damage if allowed to cool.
A very important part of the environment is the air in the laboratory. Embryos are only indirectly in contact with the air since they are grown in a special culture fluid that is covered with a layer of mineral oil. But they do need some of the gasses from the air and these simply diffuse into the oil and then the culture medium. Carbon dioxide (CO 2) is present in only tiny quantities in air (less than 1% by volume), but since it is a product of respiration it is present in the body at higher levels. We therefore supply the incubators with CO 2 to create a more physiological environment. Oxygen (O 2) is necessary too, and because air has plenty (about 21% of its volume at sea level) we don’t need to supply more. In fact, we need to take some away.
Even though we all think of O 2 as a life giving force, there is a growing body of research showing that embryos from several species do better in a low O 2 environment. Human embryos can clearly do well without a reduced oxygen environment as evidenced by the many thousands of IVF babies that have been born to date. However, it is possible that they could do better. So far the research has shown that embryos do well under low O 2 when kept in the laboratory for 5 days and transferred when they reach the blastocyst stage.
At PFC, most embryos are transferred back to patients or frozen after 3 days in the laboratory.
So far, there is no evidence that a low O 2 environment is necessary for these embryos, but we are moving towards such a modified environment for all. Currently the laboratory has 13 incubators, of which only 2 have oxygen controlling capability. These are used for the 10% of cases that are having transfers at the blastocyst stage. However, 4 more of these incubators will arrive in the laboratory this October and another 4 by year’s end. Our goal is to replace all of the current incubators by early 2006.
Those of you who take a daily vitamin pill are probably aware that antioxidants are now a common dietary supplement. We even recommend antioxidants for men hoping to improve their sperm health. Examples are beta-carotene, vitamins C and E and selenium. Oxygen is an aggressive molecule that gives rise to superoxide radicals and numerous harmful intermediates that cause cellular damage (known as oxidation). These radicals are highly reactive and they oxidize other molecules in the cell. Consequently, organisms that live in oxygen rich environments have had to evolve enzymatic systems to prevent free radical damage. Eating a varied and healthy diet will of course provide individuals with the antioxidants they need, but still some 30% of Americans are thought to take antioxidant supplements. One example of oxygen damage in the body is the oxidation of low-density lipoprotein (LDL or “bad”) cholesterol that contributes to fatty buildups in arteries.
We supply antioxidants, such as pyruvic acid or taurine, in the culture medium in which we grow embryos, and these readily mop up products of free radical breakdown such as hydrogen peroxide. But reducing environmental oxygen is now an important target and by early 2006 we will be growing all embryos in a reduced oxygen environment.
