Female Fertility by Age: Know Your Reproductive Timeline

Age is one of the factors that most influences female fertility. Although every woman has a different reproductive history, both the number and the quality of eggs naturally decline over the years, which affects one’s chances of achieving a pregnancy.

Understanding how fertility changes with age can help you make informed decisions about family planning and, when necessary, consult a fertility specialist.

Decline in Fertility with Age

Women are born with a finite number of eggs, which  naturally declines over the course of life. At birth, there are approximately one to two million oocytes. By puberty, between 300,000 and 500,000 remain. Among these, only about 400-500 will actually be ovulated during the reproductive years.

This is why we say that female fertility declines with age. As the years go by, both the number and the quality of eggs naturally decrease. One’s chances of achieving a pregnancy drop, and the risk of chromosomal abnormalities in embryos rises.

Female fertility peaks between ages 20 and 30, when a gradual decline begins in ovarian reserve, which becomes more pronounced after age 35. Although many women achieve a natural pregnancy after that age, the chances of conceiving decrease over time.

Factors That Can Accelerate Declines in Fertility

Although age is the main factor linked to declining fertility, other aspects can also affect ovarian reserve and egg quality. These include smoking, being overweight or obese, endometriosis, blocked fallopian tubes, certain hormonal disorders, polycystic ovary syndrome (PCOS). It includes also some medical treatments, such as chemotherapy or radiotherapy.

Some of these factors can be ameliorated through healthy lifestyle habits or medical treatment. However, the passage of time remains the main determinant of female fertility. Thus, knowing the state of your ovarian reserve can be useful for planning motherhood or considering fertility preservation options when necessary.

Ovarian Reserve by Age

Age is the key factor in the decline of ovarian reserve. Over the years, a woman’s ovarian reserve (the number of available eggs) decreases, as does their quality.

This reserve declines progressively, especially after age 30, affecting fertility and the ability to achieve a pregnancy naturally. Between ages 38 and 40, the impact becomes more evident. The risk of early pregnancy loss and embryos with abnormalities is higher.

In these cases, where ovarian reserve is low, or egg quality is poor, it becomes necessary to turn to assisted reproduction treatments such as IVF (In Vitro Fertilization). 

However, it is important to remember that ovarian reserve doesn’t depend solely on age. Women of the same age can show significant differences both in the number of available eggs and in their response to ovarian stimulation. Thus, assessment should always be individualized, using specific tests.

Normal Ovarian Reserve Values

Ovarian reserve can be assessed through different tests that reveal the approximate number of available eggs and help guide a woman’s reproductive outlook. These tests are especially useful when trying to conceive or before starting an assisted reproduction treatment. They help to personalize the process and to choose the most appropriate strategy.

The main tests used to assess ovarian reserve are the following:

• FSH (follicle-stimulating hormone): a hormone produced by the pituitary gland that stimulates the growth of ovarian follicles during the menstrual cycle. As ovarian reserve declines, the body needs to produce more FSH to stimulate the ovary. In general, values below 6 mIU/mL are considered normal, while figures above 13 mIU/mL may indicate a low ovarian reserve.
• AMH (anti-Müllerian hormone): one of the most widely used markers for assessing ovarian reserve, it is produced in the small follicles of the ovary, and its concentration is related to the number of available eggs. The greater the ovarian reserve, the higher the AMH levels. Conversely, values below 0.7 ng/ml are usually associated with a low ovarian reserve.
• Estradiol (E2): this hormone rises as follicles develop during the menstrual cycle. Although it reflects ovarian activity, elevated estradiol levels in the early days of the cycle (days 3 to 5) can mask a rise in FSH and be a sign of diminished ovarian reserve.
• Antral Follicle Count (AFC): a transvaginal ultrasound that counts the small follicles present in both ovaries at the start of the menstrual cycle. The antral follicle count provides a fairly accurate estimate of ovarian reserve and is one of the most widely used tests in assisted reproduction. For reliable results, it is usually performed between days 3 and 5 of the cycle.
• Ovarian volume: ovary size can also provide complementary information about ovarian reserve, as it tends to be related to the number of follicles present. In general, ovarian volume below 3 ml may suggest a decrease in ovarian reserve, although this figure should always be interpreted alongside the results of the other tests.

None of these tests, on its own, can predict the likelihood of achieving a pregnancy, but, when interpreted together by a specialist, they provide very useful information for assessing ovarian reserve and guiding the most appropriate treatment in each case.

Egg Quality by Age

A perfect egg is one that has the morphological characteristics and chromosomal makeup needed to result in a pregnancy. Abnormalities in egg morphology mean lower quality. Ultimately, however, what most affects this quality is the woman’s age, which alters the egg’s genetic makeup, but not always its morphology. This can make fertilization harder, increase the risk of miscarriage, and reduce one’s chances of achieving an ongoing pregnancy.

For example, a 45-year-old woman may have a morphologically perfect egg, yet also have a very high probability that its genetic makeup is abnormal, making its overall quality considerably lower.

Therefore, although the number of eggs matters, egg quality becomes an increasingly decisive factor with age. In fact, women with a good ovarian reserve may still have a lower chance of pregnancy if the genetic quality of their eggs has been compromised by age.

Chances of Pregnancy by Age

These figures are for general guidance and can vary depending on the characteristics of each woman and her partner. Factors such as sperm quality, ovarian reserve, medical history, and the presence of reproductive conditions can impact the likelihood of pregnancy, whether achieved naturally or through assisted reproduction techniques.

When Should You See a Fertility Specialist?

Although many women achieve natural pregnancies after age 35, seeing a specialist is recommended if you are having trouble conceiving.

In general, women under 35 are advised to seek an evaluation after one year of unprotected intercourse, and women 35 or older are advised to do so after six months. For women over 40 or when there is a history of conditions that could affect fertility, seeing a specialist may be advisable when one starts to try to conceive.

Conclusion

Female fertility naturally changes with age due to the progressive decline in ovarian reserve and egg quality. Understanding these changes makes it possible to make informed decisions about reproductive planning and to consult a specialist when necessary.

If you have questions about your fertility, or are struggling to get pregnant, a personalized evaluation can reveal the state of your ovarian reserve. This will help determine the best strategy for you. You can book an appointment with out international team.

Dr. Manuel Muñoz

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