In 2010, approximately 150,000 in-vitro fertilization (IVF) cycles were reported to the Society for Assisted Reproductive Technologies (SART) in the United States alone. As the number of couples and individuals seeking IVF services are rising, the IVF laboratory is often expected to maintain, or improve, pregnancy rates whilst adapting to evolving regulations and increases in patient volume. As IVF clinics continue to devote themselves to provide the latest in technology and services to their valued patients, a crucial component to the success of the laboratory is the selection of an appropriate embryo culture protocol and synthetic culture milieu. The modern-day embryologist is fortunate that considerable progress in the development of culture media for assisted reproductive technologies (ART) and infertility treatment has been made in the last three decades. However, truth be told is that the culture medium (some more elaborate than others) currently used in IVF are not entirely optimal and serve as a foreign environment merely to support the growth of human preimplantation embryos (Lane & Gardner 2007). However recently, a shift in the embryo culture paradigm has caused us to re-evaluate the way we grow and handle the human embryo in vitro.

The use of commercially available culture media in today’s IVF laboratory has become the standard since the early introduction and validation of one-step and multi-step culture protocols in mammalian models. The first successful development of a culture medium based on defined constituents determined by bioassay was introduced originally by Biggers (1957) and later optimized in the mouse model by Lawitts & Biggers (1991). By simultaneously providing various concentrations of components, with the effect of each ingredient dependent on the amount of other components in the mixture, the embryo itself is expected to adapt and utilize anything it requires (Summers & Biggers 2003; Biggers & Summers 2008). This principle was coined ‘let the embryo choose’, and led to the development of the KSOM family of media in which all of the substances necessary for early embryological development are present without the need for medium change (one-step) (Biggers 2002). With the addition of amino acids, KSOMAA was shown to support human embryo development from the zygote to the blastocyst stage in a one-step protocol (Biggers et. al. 2000; Biggers, & Racowsky 2002; Ho et al 2005). KSOMAA provides the core components from which Irvine Scientific’s Continuous Single Culture Media (CSCM) was formulated. However, the incorporation of the purest constituents along with refinements of exact quantities has lead to the manufacture of this newly formulated ‘one-step’ medium.

CSCM has been methodically developed and is promoted as an uninterrupted culture medium to be used in one-step embryo culture applications without disturbances. Research done by Irvine Scientific© has led to significant improvements in its composition and preparation, therebyenabling CSCM to challenge the decade-old concept that sequential media culture systems are necessary for extended culture of embryos. Two or Three-step sequential media protocols, first advocated in the human by Gardner and Lane in the late 1990’s, (Gardner & Lane 1997; 1998) are ‘naturally’ appealing as they attempt to mimic the changing needs of the developing zygote and embryo. This ‘back to nature’ philosophy was founded upon the approximate concentrations of the components thought to be similar to those commonly occurring during the physiological interactions of the embryo with the oviduct and uterus (Leese 1991; 1998).

It is true that human embryos can develop in vitro in rather different types of media: from basic systems to more complex sequential culture media. Nevertheless, the preimplantation mammalian embryo appears to be sensitive to epigenetic, metabolic, cellular, physiological and other environmental influences. Sub-optimal culture conditions and unwarranted embryonic stresses force the embryo to undergo adaptations and compensations. These avoidable adjustments can be related to poor embryo quality (Brison & Schultz 1997, Zhang et. al. 2010), and ultimately lead to lower pregnancy outcomes, higher miscarriage rates and altered birthweights (Dumoulin et. al. 2010). By moving embryos from one medium to another, unnecessary stress is placed upon the embryo through temperature, osmolality and pH fluctuations. Also, the unintentional risk of handling errors and accidental addition of contaminants are also possible, along with unwarranted shear stress through embryo pipetting (Xie et. al. 2007). Moreover, this approach is considerably more labor intensive and expensive therefore thwarting the efficiency of IVF laboratories both small and large。

In 2002, Biggers et. al. demonstrated that a ‘one step’ approach, where the embryo is cultured in an uninterrupted environment (without being moved) in the same medium, was at least as successful as when embryos were moved through sequential media in the process of extended embryo culture. This approach inherently simplified routine embryo culture with no apparent disadvantages. More recent investigations of the clinical use of Continuous Single Culture™ media, when compared to sequential media protocols, highlight a common observation that uninterrupted culture produces a higher number of blastocyst stage embryos that are thereby available for transfer or cryopreservation on day-5 of embryo culture (VerMilyea, et. al. 2012 and personal communications1,2). Similar studies also report that uninterrupted culture appears to be beneficial for blastocyst formation when compared to medium renewal on day-3 of culture (Singh, et. al. 2012).

With non-invasive technologies such as time-lapse embryo surveillance becoming more popular as tools to assist identifying the most viable embryo, the trend to reduce embryo manipulation and disruption is changing the way embryo culture is performed. Through establishing an in vitro environment that minimizes detrimental effects, which may inadvertently be placed upon an embryo, one can realize that in vitro culture is not a natural process and less, in this case, is more. By adopting a proven medium formulated for fewer disturbances, more simplification and better laboratory efficiency, Continuous Single Culture Medium can provide the near optimal environment without compromising outcomes.