Fig. 1

Schematic representation of the stages of fertilization and embryonal development. Infertility may originate from defects in production and/or functionality of gametes, fertilization, early development of the embryo, its placentation, as well as the late stages of embryonal development. Figure elements are adapted from [1, 2] and Human placental project at https://www.nichd.nih.gov/research/supported/HPP/form