Monitoring of embryos is an important activity during In Vitro Fertilization (IVF) procedures. A critical stage is that of the early embryo, which is formed by a small number of cells (blastomeres): the morphology of such cells is considered to be a powerful indicator of the embryo viability. We deal with the challenging problem of automatically segmenting the different blastomeres in the early embryo while simultaneously determining their depth, by processing a Z-stack of images acquired by means of an Hoffman Modulation Contrast (HMC) microscope.We discuss experimental results on 53 embryo image stacks, and elaborate on the advantages and limitations of our approach, also briefly describing it is being integrated in the workflow of an IVF laboratory.