Control of microinjected volume can be a problem. How do you know your injections are consistent? This paper gives a nice protocol in the supplementary online methods section.

Riedel-Kruse IH, Muller C, Oates AC. Synchrony dynamics during initiation, failure, and rescue of the segmentation clock. Science. 2007 Sep 28;317(5846):1911-5. Epub 2007 Aug 16.

The bottom line is that they are injecting into mineral oil prior to and after each group of embryos, then imaging the water droplet in the mineral oil and calculating its volume.