Owing to new insights into embryonic physiology, advanced culture media have been developed permitting in vitro incubation up to the blastocyst stage.
Incubator and culture - dishes for embryos
These innovative media minimize the detrimental effects on the viability of the embryos, which used to occur previously in prolonged culture.
The following new media are used for in vitro culture:
1. Sequential media
These media apply the principle „back to nature“:
- Medium I is used for incubation until day 3 (= 8-cell-stage). Each blastomere is like a unicellular organism.
- Medium II is used for embryo culture after compaction (morula-stage) and embryonic gene activation (paternal effect). Neighboring cells start forming cell clusters and communication between blastocyst cells is established.
The enormous differences in embryonic metabolism before and after compaction are taken into account by these new media.
2. KSOM Media
This is an optimized medium, which is referred to as „Let the Embryo Choose"- medium“, or “KCl-enriched simplex optimization medium“ (KSOM). After having intensively investigated the requirements of oocytes and embryos throughout their first days in culture, a simple optimized medium („one-step“-protocol) has been designed. International clinical studies confirmed clearly, that this medium supports effectively the development of human embryos up to blastocyst
stage. In a comprehensive prospective study the best results were achieved when using both media for culture (sequential media + KSOM). It seems that each individual embryo has its own “preferences”, which we cannot predict yet. Using this technique, we try to benefit from the advantages of both media in order to improve pregnancy rates! It is desirable to keep the embryos in culture up to day 5 (blastocyst – stage), because of the advantages outlined below:
- Culture of the most viable embryos: Applying this technique, embryos showing high developmental potential can be identified and used for transfer.
Patients exhibiting certain chromosomal disorders
might benefit from blastocyst culture, too, since specific chromosomal disorders often result in a halt of early embryonic development during a prolonged embryo culture. Blastocyst culture provides us with the opportunity to choose a viable embryo and thus improving the chances of giving birth to a healthy child.
In that context blastocyst culture is advisable for women beyond 38 years of age. The risk for aneuploidy (abnormal number of chromosomes) increases in correlation with female age. Embryos with aneuploidy tend to stop development after day 3. Higher implantation rates may be achieved by transferring one to two embryos at the blastocyst stage.
Another important advantage consists in the reduced uterine contractility from the 5th day onwards. Performing embryo transfer beyond that day may prevent the failure of the embryo to implant into the uterine wall. This was clearly confirmed by a scientific study based on measuring uterine contractions. Literature