When a baby girl is in her mother's womb, her ovaries are implanted with nearly 7 million eggs. By the time she is born, about 2 million remain. Then, over the course of childhood the number is reduced, so that when she hits puberty perhaps only 250,000-300,000 remain. More are lost every time she has a period.
女性早在娘胎時，卵巢就存放了近 700 萬個卵子，出生時約留存 200 萬個，其後在成長發育的過程還會持續減少，等青春期開始，大概就只剩下 25 ∼ 30 萬個，並隨著月經周期再繼續折損。