1000 Follicles: The Onset of Natural Menopause

Menopause, a natural part of aging in women, marks the end of menstrual cycles and fertility. This transition is a significant physiological change. Yet, menopause doesn't run on biological age, and isn't tied to other organ systems. It's tied to genetics, lifestyle and ovarian follicle reserves.

A critical factor in signaling the onset of menopause is the number of ovarian follicles a woman has. Studies indicate that reaching a threshold of approximately 1000 follicles in the ovaries can trigger the start of menopause. This article explores how this follicular threshold influences menopause and the factors that contribute to its variability.

The Role of Ovarian Follicles in Menopause

The ovaries are central to a woman's reproductive system, housing thousands of follicles, each containing an immature egg. From birth, a woman has a finite number of these follicles, which diminish in quantity and quality as she ages. The journey to menopause begins when the number of healthy follicles falls below a critical threshold, around 1000. This decrease results in reduced estrogen production, leading to the cessation of menstrual cycles and the onset of menopause.

Genetic and Environmental Influences

The age at which a woman reaches this follicular threshold, and consequently menopause, is influenced by a combination of genetic and environmental factors. Genetics play a significant role (about 50% of the age of natural menopause is determined by genetics), with family history often being a predictor of menopausal age. Environmental factors, such as stress, obesity, shift work, smoking and certain medical treatments, can also impact follicle quantity, accelerating or delaying the onset of menopause.

The Physiological Process 

As the number of follicles declines, the body undergoes hormonal adjustments. The ovaries gradually produce less estrogen, leading to a range of menopausal symptoms like hot flashes, mood swings, and changes in menstrual patterns. This hormonal shift also affects other bodily systems, contributing to long-term health considerations like bone density and cardiovascular health.

Is There Any Way to Know How Many Follicles Remain?

There are methods to estimate the number of ovarian follicles a woman has, which can provide insight into her ovarian reserve—the number of remaining eggs in the ovaries. However, it's important to note that these methods offer estimates rather than precise counts.

Here are the primary ways to assess ovarian reserve:

1. Antral Follicle Count (AFC): This is a transvaginal ultrasound procedure used to count the number of antral follicles (small follicles) in the ovaries at a specific time in the menstrual cycle. Antral follicles are considered a good indicator of the remaining ovarian reserve. While AFC is commonly used in fertility assessments, a significantly low count could suggest that a woman is nearing menopause, as it indicates a diminished ovarian reserve.

2. Anti-Müllerian Hormone (AMH) Test: AMH is a hormone produced by the cells of antral and pre-antral follicles. The levels of AMH in the blood can give an indication of the number of follicles. Generally, lower levels of AMH suggest a lower ovarian reserve. Low AMH levels can indicate a reduced ovarian reserve, which might suggest that a woman is approaching perimenopause. However, AMH alone is not a definitive indicator of menopause onset.

3. Follicle Stimulating Hormone (FSH) Test: This blood test is typically done on the third day of a woman's menstrual cycle. Elevated levels of FSH can be an indicator of a declining ovarian reserve. However, FSH levels can fluctuate and may not always provide a consistent indication of ovarian reserve. Elevated FSH levels, especially when combined with other clinical symptoms, can be indicative of perimenopause. FSH levels typically rise as the ovaries start to produce less estrogen.

4. Clomiphene Citrate Challenge Test (CCCT): This test involves measuring the levels of FSH on the third day of the menstrual cycle, administering clomiphene citrate (a fertility medication), and then measuring FSH levels again on the tenth day. The response to this challenge provides information about the ovarian reserve. While CCCT is more focused on fertility potential, abnormal results can also indicate declining ovarian function, which is associated with perimenopause.

5. Ovarian Volume Measurement: Sometimes, the overall volume of the ovaries, measured through ultrasound, can give clues about the ovarian reserve. Smaller ovaries may indicate a reduced reserve. This is less commonly used for determining menopausal status but can provide additional context in the assessment of ovarian aging.

Perimenopause, which on average lasts 7 years (but can be up to 12 years), is the time when the folllicular supply decreases. By knowing where a woman is in her follicular supply, the more control she will have over her reproductive timing and choices.