At what age does fertility begin to decrease?

Girls are born with a fixed number of immature eggs in their ovaries. The number of eggs decreases as women get older. At birth, most girls have about 2 million eggs, at adolescence that number has gone down to about 400, 000, at age 37 there remain about 25,000. By age 51 when women have their menopause they have about 1000 immature eggs but these are not fertile. At every menstrual cycle one of the immature eggs will mature and be released during ovulation. The eggs that are not released die and get re-absorbed into the body. The quality of the eggs also gets poorer as women get older. All other things being equal the number and quality of the woman’s eggs determines her fertility.

Monthly fertility rate by age

Adapted by permission from BMJ Publishing Group Limited. [Delaying childbearing: e ect of age on fecundity and outcome of pregnancy, van Noord-Zaadstra et al., 302, p. 1363, 1991]

Graphic 3 shows that on average there is a decline in female fertility starting in the mid-thirties, with lower fertility especially after the age of 35. Women’s fertility will continue to decrease every year, whether or not she is healthy and fit because the number and quality of the eggs decreases with age. Even if a woman is not ovulating (for example if she is taking the contraceptive pill, or is pregnant), the number of eggs continues to decline at the same rate. How quick a woman’s fertility declines will depend on a combination of genetic and lifestyle (e.g. smoking) factors.

Men are not born with their sperm. Men produce sperm daily. Men’s fertility also starts to decline around age 40 to 45 years. The decrease in fertility is caused by the decrease in the number and quality of the sperm they produce. Men can have fertility problems even if they can still have sex and have an ejaculation.

If you are concerned about your age and your fertility, you may consider having your fertility tested. Fertility tests for men and women are available at pharmacies, online and at fertility clinics. You can discuss your fertility with your doctor.

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