Age and Fertility

Eggs: A Limited Resource

Women are born with millions of eggs. For unknown reasons, most of these eggs die before they ever have a chance to mature and ovulate. About 1,000 eggs die for every egg that matures and is released. This decline is part of the natural aging process. Importantly, egg quality also diminishes with time, with miscarriages and chromosome defects becoming more common with later age at pregnancy.

In reproductive-age women, about 5–25 eggs are present in each cycle. These "finalists" can respond to FSH and mature. As it turns out, however, humans have natural mechanisms that keep all but one of these finalists from growing, which means only one egg will be ovulated, except in the case of fraternal twins and triplets.

Very few eggs remain at menopause, which occurs on average at age 51. Remaining eggs no longer respond to FSH. Menopause is the absolute end of the reproductive years. However, women typically lose the ability to conceive in their early 40s, about 5–10 years before ovulation and menstruation finally ends.

In your 20s

A large number of high-quality eggs are found in a woman's mid-20s, so the best future outcomes result from eggs stored at this age. With the help of Preimplantation Genetic Testing for aneuploidy (PGT-A), we know these eggs are highest quality because they have the greatest potential to produce healthy euploid embryos—those that contain a normal number of chromosomes. A 25-year-old doing in vitro fertilization produces an average of about 6 healthy euploid embryos per treatment cycle out of 12–18 eggs.

In your 30s

The eggs of women in their early- to mid-30s produce progressively fewer euploid embryos. Between ages 30–35, women produce an average of 3 euploid embryos. Between ages 38–40, they produce 1 euploid embryo on average.

In your 40s

At this age, less than one healthy euploid embryo is found per cycle. For women choosing to delay conception, there may be some benefit of egg freezing as early as possible.

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