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
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
What CO2 concentration should be used with global®
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
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.