Egg supply is an important factor that affects fertility for every woman: the more eggs you have, the higher likelihood you will be able to get pregnant. As you are learning about fertility and conception, it’s helpful to know how your eggs play a role in bringing a baby into your family.
Female Eggs are Finite
When a female baby is born, she comes into the world with all the eggs she will ever have. These eggs are located in the ovaries – and there will be no new eggs created during her lifetime. This number is finite, which means that a woman has limited opportunities for pregnancy. This differs from men, who can produce an infinite amount of sperm.
The immature eggs at birth are called oocytes, which are located in sacs filled with fluid (known as follicles). The oocytes remain in the ovaries until the maturation process begins, when it eventually develops into an ovum (a mature egg). To keep it simple, we will refer to the term most commonly used: egg.
Eggs at Birth
In the earliest stages of development, it is estimated that a female fetus has as many as 6 million eggs. These eggs reduce steadily over time, with approximately 1 – 2 million eggs remaining at birth. Various sources have differing opinions about the exact number of eggs at the time of birth, but most experts agree that female newborns have at least a million eggs.
Even though these eggs are present, they are still in the oocyte stage, which is why the menstrual cycle doesn’t begin for infants or young children. This menstrual process is on hold until the child reaches puberty. It is necessary for the brain to produce two hormones that affect estrogen levels:
- Gonadotropin-releasing hormone (GnRH)
- Follicle-stimulating hormone (FSH)
As the hormone levels change, they play a role in puberty and fertility – as well as the development of oocytes into mature eggs. The average age of menstruation is 12 years old, although it ranges between 8 and 15 years old.
Egg Counts from Puberty into the 20s
When puberty is reached, it is estimated that between 300,000 and 400,000 eggs remain. In the earliest years of life, more than 10,000 eggs die monthly, which reduces the overall number of eggs over time. This process slows when puberty is reached. Once the menstrual cycle begins, it is estimated that a woman loses about 1,000 eggs each month (between 30 – 35 eggs per day).
Doctors aren’t sure why this change occurs at puberty. From what they’ve learned so far, it appears that egg die-off is not affected by health, hormone levels, or nutrition. A few lifestyle factors can speed up egg loss, such as smoking or chemotherapy/radiation treatments.
After puberty, these eggs are sensitive to the hormone fluctuations throughout the month. Even though multiple eggs are dying each day, only one egg reaches a point of ovulation – which triggers the menstrual flow for the month.
In her 20’s, a woman is most fertile because her egg counts are still high – and these eggs are healthy. This fertility continues into her early 30s, then fertility begins to decline in the mid-30s.
Egg Counts in 30s and 40s
The egg count decreases over time, which means that only a portion of the eggs is left in the 30s. For example, a woman might have only 25,000 eggs left by the time she is 37. Again, the exact numbers vary, depending on the resource, but the numbers show how the eggs decline with age.
At the age of 40, there isn’t one exact number of eggs remaining at this point, because the egg count varies from one woman to the next. If you’ve avoided certain lifestyle habits, such as smoking, then it’s possible that you have more eggs compared to other women who smoke regularly.
A woman in her 40s can still get pregnant, but there is less than a 5% chance of pregnancy happening with each menstrual cycle. Compare this rate to the 25% likelihood in the early 20s, and you can see how much age plays a role in conception and fertility.
When menopause is reached, it means that no eggs are left and a natural conception is no longer an option. At this point, the ovaries no longer create estrogen, which causes hormonal changes in the body to stop menstruation. The average age for menopause is 52, although some women start experiencing symptoms of menopause in their 40s. The specific age you reach menopause depends on the number of eggs present at birth, as well as the rate of egg loss over time. For example, women who are able to have natural pregnancies in their mid- to late-40s likely had a higher egg count at birth.
Egg Quality with Age
Women considering pregnancy in her late 30s and early 40s not only need to be aware of the number of eggs remaining at this point, but it’s also important to note the quality of these remaining eggs. The highest quality eggs are ovulated in the earlier years of life, leaving the older, lower quality eggs as the years pass by.
Older eggs have a higher risk of genetic problems, which means there is a higher risk of chromosome abnormalities. For example, the risk of the child having developmental issues or Down syndrome increases with age.
Of course, there still may be healthy eggs present for a woman. But the risk of complications increases with pregnancy in the late 30s and early 40s.
Egg Count and Pregnancy
Just because the egg count is continuously reducing doesn’t mean there isn’t an opportunity for pregnancy. This process is natural and continuous, but it is important to understand that the likelihood of a healthy pregnancy is much higher in the early years of life. Learning about these changes over time can help a woman decide on the right timing for conception and pregnancy.
Knowing the numbers means that you can discuss your pregnancy options with your doctor, and also determine the right timing for conception. Many women are motivated by their ticking biological clocks, which is why it is important to consider age if you’d like to have a natural pregnancy.
When the natural fertility cycles come to an end, reproductive technologies can be used to help women in their 40s or even 50s get pregnant. Modern technology can be used to intervene, using treatments such as in vitro fertilization. After the early 40s, IVF using a woman’s eggs is unlikely, but some women choose the use of donor eggs to conceive in the later years of life. These fertility treatments are also sometimes used for younger women as well who are having difficulty getting pregnant. For more info read Age & Fertility – When are Women Most Fertile?.
Fertility doctors can assist with tests to predict ovarian reserve, and also measure the hormone levels during the menstrual cycle. These tests are measurements to determine the possibility of natural pregnancy, and whether interventions are needed to support conception.
Ultimately, the best solution is to talk to your doctor as early as possible about your fertility plans. It’s important for every woman to know how fertility changes over time. This information can be empowering to plan the right timing for conception and pregnancy, especially if multiple pregnancies are desired.
