P–168 RCT comparing the effect of Continuous ( Single Step ) embryo culture system versus a Sequential embryo culture system on the outcome of IVF/ICSI cycles
Authors: Singh R , Singh M 
Published: August 2021

Study question

Is the outcome of IVF/ICSI cycles done with continuous (single step ) embryo culture system different from that with sequential embryo culture system ?

Summary answer

Yes the outcome of IVF / ICSI cycles done with continuous (single step ) embryo-culture system is better than that with sequential embryo-culture system .

What is known already

Embryo culture media are important factors in IVF, which can significantly influence the clinical outcome of IVF/ICSI cycles. However it is not clear which formulation is most optimal and whether sequential or continuous media (single step) should be favored. Sequential media complies with embryo demands based on developmental stage , taking into account metabolic changes embryos undergo in-vivo, while moving from the oviduct to the uterus. The embryos in the early cleavage stage prefer to use pyruvate to produce energy, whereas once development nears the blastocyst stage , the embryos start using glucose in the process of glycolysis .

Study design, size, duration

A prospective RCT was carried out at our centre between 2018–2019 and IVF-ICSI patients meeting inclusion criteria (at least six normal MII - Oocytes) were included in this study. The aim of study was to compare blastocyst formation rates after embryo-culture in two different culture media systems. 436 metaphase II Oocytes from 62 women were randomly and equally divided to be fertilized and cultured to the blastocyst stage in either sequential media or single-step media.

Participants/materials, setting, methods

In this prospective trial with sibling oocytes, 436 metaphase II oocytes from 62 women were randomly and equally divided to be fertilized and cultured to the blastocyst stage in either sequential media ( n = 218 MII oocytes) or a single medium ( n = 218 MII oocytes). In both groups, embryos were cultured in an interrupted fashion with media changes on day 3. Embryo transfer was performed on day 5.

Main results and the role of chance

Blastocyst formation rates on day 5 were significantly higher following culture in single step media 60.55% (132 / 218 ) as compared to sequential media 34.86% ( 76 / 218) . The percentage of good quality blastocysts was also significantly higher in single step media. In conclusion, culture in single step media was associated with higher blastocyst formation rates compared to sequential media , suggesting that the single medium may provide better support to the developing embryo. The proportion of poor quality embryos was significantly higher in the sequential media group. Results indicate that embryo culture in continuous media could be as efficient as embryo culture in sequential media. A significant difference observed was the proportion of poor quality embryos on day 5 , which was significantly higher when the embryos were cultured in sequential media. Our results suggest that the type of embryo culture media can influence the quality of embryos both at the cleavage stage and blastocyst stage. The use of continuous embryo culture media does not seem to cause an adverse effect; in fact, their use can lower the workload in busy IVF labs and lower the stress that embryos are exposed to during handling.

Limitations, reasons for caution

Although single-step-medium for extended culture has practical advantages and blastocyst formation rates appear to be higher, there is insufficient evidence to recommend either sequential or single-step media as being superior for the embryo-culture to days 5/6. Further studies comparing these two media systems in well-designed trials should be performed.

Wider implications of the findings: When employing sequential media for embryo culture , it is necessary to transfer the embryos from one medium to another ( cleavage stage medium to blastocyst stage medium) which increases stress related embryo damage . Therefore, single-step media is beneficial as the embryos can develop undisturbed till blastocyst stage.

Trial registration number

Not applicable