5 Key Insights on Ovarian Reserve and Fertility: Understanding Your Ovaries from Birth to Menopause

Understanding ovarian reserve and fertility is essential for every woman who wants to know how her reproductive system works and what affects her ability to conceive. Your ovaries hold a finite number of eggs, and how they develop, release eggs, and decline over time plays a huge role in fertility. This article breaks down the journey of your eggs from before birth through menopause, explains the hormones that controls ovulation, and clarifies common questions about birth control, ovarian reserve testing, and aging.

Table of Contents

• 1. Your Ovaries' Egg Bank
• 2. Egg Loss from Fetus to Menopause
• 3. Birth Control and Its Impact on Egg Loss
• 4. Ovarian Reserve Testing: What the Numbers Mean
• FAQ: Common Questions About Ovarian Reserve and Fertility
• Conclusion

1. Your Ovaries' Egg Bank

The ovaries contains all the eggs you will ever have in your lifetime. Your eggs actually begins before you were born. At around five months in the womb, a female fetus has about six to seven million eggs inside her ovaries. However, most of these eggs don't survive.

By the time you are born, that number drops dramatically to about one to two million eggs. As you grow and approach puberty, the number decreases further to around 100,000 to 200,000 eggs. Despite this large number, you will only ovulate approximately 400 eggs during your life. This means the vast majority of your eggs will never mature or be released.

Every month, your ovaries send out a group of eggs from ovaries. This process happens even before you start having periods. The eggs develop inside tiny sacs called follicles, which can be seen on ultrasound, but the eggs themselves are microscopic. When your ovary is full, it releases more eggs monthly. When the vault starts to empty, fewer eggs are released.

Think of the ovaries as having a keeper who controls how many eggs leave each month. When the it is full, the keeper lets more eggs out. As the vault empties, fewer eggs are allowed to leave. This natural decline is unavoidable and happens at its fastest rate before birth.

2. Egg Loss from Fetus to Menopause

The most rapid loss of eggs happens before birth, from the five-month fetal stage to birth. This means the environment your mother was in during pregnancy impacts your egg count. Factors such as genetics and epigenetics (how genes are turned on or off by environmental factors) can program the number of eggs you start life with.

After birth, eggs continue to die off throughout childhood, even before puberty starts. During prepuberty, there is no follicle-stimulating hormone (FSH) to promote egg growth, so eggs keep dying without being released.

Puberty is more than just getting your first period. It is a complex process involving the brain, ovaries, and adrenal glands. Your brain senses that your body has reached a certain weight and nutrition level and starts producing FSH. This hormone signals your ovaries to grow eggs and produce estrogen, which triggers physical changes like breast development and pubic hair growth.

3. Birth Control and Its Impact on Egg Loss

Many people believe that using birth control pills saves eggs, but this is a myth. Birth control pills contain synthetic estrogen and progestin, which trick the brain into thinking there is already a follicle growing. This prevents the brain from releasing FSH and stops ovulation.

However, the ovaries continues to release eggs each month regardless of birth control use. The eggs that come out but don't ovulate simply die off. So, birth control pills do not preserve your egg count; your eggs continue to decline naturally over time.

The same is true during pregnancy and breastfeeding. Even though you are not ovulating during these times, eggs are still being lost from the ovaries.

4. Ovarian Reserve Testing: What the Numbers Mean

Ovarian reserve tests help estimate how many eggs you have left in the vault by measuring hormones and counting follicles visible on ultrasound. The most common test is the Anti-Müllerian Hormone (AMH) blood test, which measures hormone levels produced by the cells surrounding the eggs in the follicles.

Higher AMH levels usually mean more eggs. For example:

• At age 30, a normal AMH is about 2 to 4 ng/mL with around 20 antral follicles.
• At age 35, normal AMH is about 1.5 to 3 ng/mL with around 15 antral follicles.
• At age 40, normal AMH is about 1 to 1.5 ng/mL with around 10 antral follicles.

These numbers naturally decline as you age. However, AMH and follicle counts can vary month to month by up to 30%, so a single test is only a snapshot, not a full picture of your fertility trend.

It's important to understand that a low AMH alone does not mean you are infertile. If you are ovulating regularly and have a normal menstrual cycle, your chance of getting pregnant is mostly related to your age rather than your egg count.

Ovarian reserve testing helps identify if your egg count is lower than expected for your age and can guide fertility planning and treatment.

FAQ: Common Questions About Ovarian Reserve and Fertility

How many eggs are you born with?

You are born with about 1 to 2 million eggs, which is already a decline from the 6 to 7 million eggs you had at five months in the womb.

Does birth control preserve eggs?

No, birth control pills prevent ovulation but do not stop egg loss. Eggs continue to leave the vault and die off every month.

When do you start ovulating?

Ovulation typically starts after puberty begins, following a period where estrogen levels rise without ovulation. The brain then sends signals to trigger ovulation once follicles mature.

What is the corpus luteum?

The corpus luteum is the structure formed from the follicle after it releases an egg. It produces progesterone to prepare the uterus for pregnancy.

How does ovarian reserve testing work?

Tests like AMH measure hormones from the follicles surrounding eggs. Higher AMH levels usually indicate a higher egg count. Antral follicle count via ultrasound is also used to estimate ovarian reserve.

Does egg freezing or IVF reduce your egg count?

No, these procedures only retrieve eggs that would have been lost naturally that month. They do not speed up the decline of your ovarian reserve.

How does menopause affect your cycle?

As egg count declines near menopause, menstrual cycles become irregular, often shorter at first, then longer with skipped periods until menstruation stops for 12 months, which defines menopause.

Conclusion

Understanding ovarian reserve and fertility helps you better grasp how your body's egg supply works from birth to menopause. Your egg count starts high in the womb but naturally declines throughout life. Hormones from the brain, ovaries, and adrenal glands control egg growth, ovulation, and menstrual cycles. Birth control and pregnancy do not preserve eggs, and ovarian reserve testing provides useful but limited insight into fertility potential. By knowing these facts, you can make informed decisions about your reproductive health and fertility planning.