From ovulation to adplantation

Fertilization and pre-implantation occur in the uterine tube, on the way to the implantation site. After ovulation, the oocyte is captured by the fimbriae of the fallopian tube (day -1). Fertilization (hour 0) normally takes place in the ampulla (+8 hours, the zygote is in the pronucleus stage; +16 hours, the zygote is in the metaphase). Cell divisions take the zygote through the 2-cell (1st day), 4-cell (2nd day), 8-cell (3rd day) and 16-cell (4th day) stages of the blastomere. The blastocyst then attaches to the uterine mucosa (5th day) and begins penetration (7th day).