When the “biological clock” stops, and why!

When we talk about women’s “biological clock” we really are talking about a woman’s ovarian reserve, which diminishes over the course of every woman’s life until menopause. In contrast to men who produce new sperm on a daily basis throughout their lives, a woman is born with approximately 1-2 million immature eggs, or follicles, in her ovaries. As she ages, her egg supply, or ovarian reserve, decreases significantly. By the time a girl reaches puberty, she will have approximately 300,000-400,000 eggs left in her ovaries. As she approaches 30 years of age, only 12% of her original egg supply will remain. After the age of 35, a woman’s ovarian reserve begins to rapidly decline, so that by the age of 40, she will have only 3% of her eggs remaining. Menopause occurs at the end of the reproductive lifespan when a woman’s egg supply is fully depleted, at which time her menstrual cycle ends – on average around age 51. However, because of genetics, illness or medical procedures, some women go through menopause “prematurely” – sometimes before the age of 40.

Over the course of a woman’s reproductive life span, the majority of follicles will degenerate through a process called astresia. Roughly 1000 eggs die during a woman’s menstrual cycle; only one will mature into an egg, or ovum. Therefore, a woman will only release about 300-400 mature eggs during her entire reproductive years! Also with advancing age, the quality of a woman’s eggs decreases. That’s one of the reasons there are higher rates of Down’s Syndrome among babies born to women in their 40s, and higher rates of miscarriage.

Read more about age-related female fertility decline here.

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One Response to “When the “biological clock” stops, and why!”

  1. Norah says:

    I am now approaching 30, and I wish I could slow down my biological clock! I know I have some time before my fertility really starts to decline, but I’m starting to get scared that i won’t meet someone, and won’t be able to have kids in the way i always thought i would — in a loving, long-term relationship. I suppose time will tell. I knew fertility declined with age, but I didn’t know all the details you have presented here. Thanks for the info!

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