Introduction:

Time lapse imaging (TLI) incubators have revolutionised our understanding of early human embryonic development but their role in clinical laboratory practice remains uncertain. Algorithms have been generated using the information gained from more detailed knowledge of embryo development such as cell division timings (embryo morphokinetics). However, the application of these algorithms to improve embryo selection appears to be hindered by the lack of translatability across laboratories, probably reflective of inter-laboratory variation1. Additionally, embryos possess the potential of auto-correction whereby some embryos with abnormal initial morphokinetics go on to form good quality blastocysts. These auto-correcting embryos appear to have a better prognosis than embryos which fail to form good quality blastocysts 2.
Another school of thought is to use the data derived from TLI incubators as subservient to conventional morphological assessment by using the morphokinetic data as exclusion criteria. This enables differentiation between embryos of similar morphology when choosing the best embryo to transfer 3.
By obviating the need for the embryo to be removed from the incubator for morphological assessment, TLI incubators provide a more stable culture environment. Previous research from our unit indicated that this more stable culture environment might contribute to superior perinatal outcomes with babies born from embryos cultured in TLI incubators having a lower risk of preterm birth and low birth weight 4. However, there was no difference in cumulative live birth rate. Sequential culture medium had been utilised during the period of that study which required the TLI incubator doors to be opened on the third day of culture for media change. Since November 2015, the culture medium was changed to single step culture medium which allowed for truly uninterrupted culture in TLI incubators until the day of embryo transfer.
Guidance from the British Fertility Society (BFS) 5, European Society for Human Reproduction and Embryology (ESHRE)6 and the Human Fertilisation and Embryology Authority (HFEA) 7 on the role of TLI incubators in current IVF practice reflects the uncertainty associated with TLI use. Particular criticism has been directed on the absence of cumulative live birth data which would help assess whether the role of TLI incubators is improving embryo selection or whether it improves the culture environment in addition to better embryo selection 6.
The aim of this retrospective study is to compare the cumulative live birth rate between TLI and standard culture (SC) incubators with the use of single-step culture medium.