Fertilization vs Culture: Which medium to choose?
Introduced more than 20 years ago, Universal IVF Medium has become one of the most popular, tried and tested IVF media on the market. Culture media have since advanced into richer, more composite products, optimized towards human embryo physiology and development. A modern culture medium, such as ISM^TM,  is a complex fluid supplying amino acids, nucleotides, vitamins, and metabolites adjusted specifically to each stage in embryo development.

Fertilization: High metabolism = high energy source
The relatively brief process of IVF fertilization has different physiological requirements compared to culture. Fertilization requires higher sperm energy supplements for the metabolically demanding capacitation, hyperactivation, acrosome reaction, sperm-egg fusion. Universal IVF Medium contains high levels of glucose to best support fertilization.

Culture: Mimicking nature - what does the embryo need?
High glucose is not optimal for Day2-Day3 culture, since the embryo is unable to properly metabolise glucose at this time. ISM^TM is a complex, low-glucose medium, giving significantly better culture conditions for the embryo.

The advantage of using advanced media for embryo culture, and high glucose for fertilization is well known and documented (see below).

Documentation
A 216-patient multicenter sibling study by Erb et al 2004 comparing sibling oocytes cultured in Universal IVF Medium and ISM1™, resulted in significantly better fertilization rates in Universal IVF Medium, and significantly more ‘good quality’ embryos for both fresh transfer and cryo in ISM1™.

Figures 1 and 2. Erb et al 2004

 

This result was supported in a 732-cycle study by Michaeli et al 2007, comparing fertilization and culture in Universal IVF Medium, ISM1™, and P1 Medium. Of the three media, Universal IVF Medium yields significatly higher fertilization, while ISM1™ yields both significantly higher percentage of normal/fast cleaving embryos and implantation rate.

 

 

 

Figure3. Michaelli et al 2007

The authors conclude: “It seems that the presence of higher concentration of glucose in the medium (Universal IVF) is necessary for improving fertilization rate...” “...Moderate glucose concentration (ISM1) could be beneficial for obtaining higher developed embryos, when being transferred could improve implantation rate”.”

In a 141 cycle study, Steele et al 2006 showed significantly more good quality embryos and significantly higher pregnancy rates in ISM1 vs Universal IVF. The authors conclude that “ISM culture to Day 2 supported faster embryo deveopment, better embryo quality, and a higher clinical pregnancy rate”.

A very recent 726-patient comparison study by Xella et al 2009 has again confirmed the above results by showing significantly more good-quality embryos, ongoing pregnancy rates, and implantation rates when culturing in ISM^TM vs Universal IVF Medium. 

 

 
Figure 4. Xella et al 2009

The authors suggest that: “ISM1 Medium appears to be more efficient in improving embryo quality with respect to Universal IVF Medium during the in vitro culture period […] Universal IVF Medium, used as a monoculture medium, should be replaced by ISM1™ Medium after the fertilization check, with the supplemented ISM1™ components seeming to better sustain in vitro embryo growth”.

Final notes:
IVF fertilization and culture should be viewed as different procedures. Fertilization requires a medium corresponding to the high metabolic needs of especially the spermatozoa.  Culture media must support the advancing needs of the embryo as it develops from the low-metabolism zygote and cleavage-stages without an active genome into a highly metabolically active morula and blastocyst.

Universal IVF Medium is a high-glucose medium – probably the best fertilization medium in the world.
ISM1™ is an advanced cleavage-stage culture medium, designed to mimic the natural environment of the embryo.

References:

Erb, K et al 2004: A multicenter study comparing sibling oocytes cultured in ISM1TM versus Universal IVF Medium". Study available from MediCult here

Michaeli et al 2007: In vitro fertilization outcome using three types of culture media containing different concentrations of glucose for developing cleavage stage embryos. A comparative study. Fertility and Sterility 88(suppl 1):S324

Steele et al 2006: Comparison of MediCult Sequential Medium ISM1 with Non-Sequential Universal IVF Medium in an IVF/ICSI Programme. British Fertility Society Summer College, Oral communication (OC12).

Xella et al 2009: Embryo quality and implantation rate in two different culture media: ISM1 versus Universal IVF Medium. Fertlity and Sterility (epub ahead of print)