Questions about global® Medium answered by our Scientific Team

How can global®, a single medium, fully support both early cleavage of human embryos, and subsequent development to the blastocyst stage?

It has been suggested that the chemical environment of the oviduct is different from that of the uterus and therefore human embryos must be sequentially cultured in (at least) two different media to reflect the difference in the in-vivo environments. However, it is very doubtful that the measurements of the composition of oviduct and uterine fluids reflect the micro-environment of the embryo in vivo. Moreover, the environment in culture is physically very different from that in the reproductive tract, and embryo culture media must be designed to optimize embryo development in culture. Moving the embryo to a second medium is a stress upon the embryo. Many clinical studies have shown that single media, most notably global®, support the development of human embryos as well or better than do sequential culture media systems.

Why does global® medium contain glucose?

The concern about glucose in embryo culture medium originated from the observation that the cleavage of hamster embryos was inhibited by glucose when present in the medium with phosphate. This has shown not to be the case for a variety of media, and a variety of species. If fact, some source of glucose is absolutely required for development of the embryo at all stages. It was for this reason that glucose was included in the basic set of constituents used in the simplex optimization development of KSOM-AA, the medium upon which global® is based.

Does ammonium build up in global® medium?

The major potential source of ammonium in embryo culture medium is glutamine. It is for this reason that glycyl-glutamine is used as the source of glutamine in global®. It has been shown that there is very little or no accumulation of ammonium in embryo culture media that contain glutamine dipeptide rather than glutamine.

Why does global® medium contain EDTA?

EDTA was first shown to be beneficial for the culture of mouse embryos by Abramczuk et al. in 1977, and has been included in most embryo culture media since then. The exact mechanism of action of EDTA is not clear, but is generally thought to chelate iron and other divalent cations which can induce the production of toxic reactive oxygen species.

Why does global® medium contain Phenol Red?

Phenol Red is a pH indicator and is included in global® to serve as a rapid visual check that the CO2-bicarbonate buffer system is functioning. However, the exact pH should be systematically monitored with a pH meter (see below). It has been suggested that Phenol Red may be toxic to embryos but there is absolutely no scientific evidence to support that suggestion. The one study that specifically examined the effect of Phenol Red, showed that it had no effect on the development of hamster embryos.

What CO2 concentration should be used with global® medium?

In most cases, a 5-6% concentration of CO2 in the incubator will produce a pH of 7.2 to 7.4 in HSA-supplemented global® medium. However, the exact concentration of CO2 required to produce the optimum pH of 7.3 depends on several factors, including the altitude and the characteristics of the HSA used for protein supplementation. Consequently, we strongly recommend that each laboratory determine and use the exact concentration of CO2 that is required to produce a pH of 7.3 in HSA-supplemented global® medium.

Why does global® medium become a darker red after the bottle is opened?

During manufacture, global® is bubbled with CO2. Each time the bottle is opened, CO2 escapes from the medium into the head space and from there into the atmosphere. Consequently, the medium in the bottle becomes slightly more basic and the Phenol Red indication becomes a darker red. This has no effect on the medium. When the medium is placed in a CO2 incubator, it absorbs the CO2, and the proper pH is established.

Why does global® medium not contain HSA?

HSA is not included in global® for two reasons. First, HSA is a biological component and consequently the quality control requirements are different from those for the chemical components. Second, the optimum concentration of HSA in embryo culture medium depends on the laboratory procedures, which differ between IVF laboratories. By not including HSA in global, each laboratory can supplement it with HSA to the concentration that is optimal for the laboratory's conditions.

Why is the shelf-life of LifeGlobal culture media 10 weeks from the date of manufacture?

Some of components of embryo culture media, including the amino acids and pyruvate, are subject to oxidation or spontaneous degradation. Consequently, we limit the shelf-life of our embryo culture media to ensure the best performance possible. Moreover, we manufacture our media at least once per month, so that fresh media are always available to you.