Oogenesis is the process by which female gametes (ova/eggs) are formed. It begins during fetal development with primordial germ cells that migrate and undergo mitotic division, resulting in around 7 million primary oocytes by the 8th week of gestation. These enter meiotic arrest in prophase I. Folluculogenesis is the growth and maturation of follicles containing the ova. It occurs in four stages from primordial to tertiary follicles, with the late tertiary follicle being around 20mm and containing the nearly mature ovum.