Embryo culture drop size – is there an optimum?

We recently had an excellent question from one of our clients, who wanted to know if our recommendation of 5 micro-litres (uL) of medium per embryo cultured was critical or not, or could it be changed to suit their IVP embryo production system.  Firstly, our protocol recommendations are based on our long-history of research and commercial application with the media formulations we have, and this is why we provide our preferred protocol.

The optimal medium volume per embryo cultured really depends on several factors: breed of cattle; culture vessel; oxygen concentration (we ALWAYS recommend 5-7% oxygen for all stages of embryo culture); numbers of embryos being cultured in one container or drop; medium buffering system; use of oil and rate of evaporation in the absence of oil; use of additives such as growth factors or serum.

Given all of that, we err on the cautionary side and recommend a relatively large volume per embryo cultured, given that we recommend our sequential medium system.   Experimentally, we culture 4-5 embryos per 20uL microdrop under paraffin oil (MEA/BEA tested).  If you want to explore using larger embryo groups, you may find reducing the volume size from 5uL/embryo to even as low as 2 uL/embryo could be beneficial.  We would not recommend even lower media: embryo ratios.  One reason we use 4-5 embryos/20uL is that at transition to VitroBlast medium, we group the best embryos with each other – this provides more            opportunity for the best embryos to benefit from the autocrine/paracrine growth factors    produced by the embryos themselves.  These will also be the most metabolically active, and therefore will be more ‘draining’ of the medium’s substrates.  This will also be a factor if you have residual cumulus cells that remain on the embryo and even plate down. These additional cells will definitely ‘drain’ the medium of substrates.  It wouldn’t be an issue at 5uL per embryo, but may at low volume/embryo grouping.

As always, we cannot guarantee results and take no liability for your embryo production and transfer outcomes.

If you have a question for the ART Lab Solutions team contact us directly at admin@artlabsolutions.com.