When does oogenesis typically begin in females?

Oogenesis is the process of egg (oocyte) development in females, which begins before birth. This process starts in the female fetus during the early stages of development, where primordial germ cells in the ovary undergo mitotic divisions to form primary oocytes. These primary oocytes then enter prophase of meiosis but remain arrested at this stage until puberty.

At birth, females have a finite number of primary oocytes that constitute the ovarian reserve. As females progress through childhood into puberty, these primary oocytes can resume meiosis during the menstrual cycle, but the initial formation of oocytes occurs at birth. This foundational concept in reproductive biology underlines the importance of early development in female fertility and the limited number of eggs females have throughout their reproductive years.