ABSTRACT
The typical course of development following normal fertilization of the human egg in vitro begins with completion of second meiosis, extrusion of a polar body (PB2), and the emergence of one male and one female pronucleus some 9-11 hours later (day 1). Development continues with three to four mitotic divisions in the following 48 hours, producing an embryo with 2-4 (on day 2), and 8-10 (on day 3) roughly equal-sized mononucleated cells; division continues followed by compaction of the cells on day 4, and cavitation and differentiation of the embryo into two distinct cell types – inner cell mass and trophectoderm – between days 4 and 6 of development (Figure 6.1).
