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.