One of the questions I get often as a fertility expert is this:
Since fertility medications get multiple eggs to develop at once, will this cause a person
to run out of eggs sooner? Or the opposite, will using birth control pills to block ovulation save
more of your eggs for when you are older. Stay tuned as I answer these interesting questions.
First, some basic biology. Eggs are produced in the ovaries while a person is a fetus.
Initially, the number of eggs in the ovaries increases up to a few million. But about three
months before birth, all egg production stops. After this time, no new eggs will
be formed in the ovaries. Therefore, the number of eggs in the ovaries is finite.
Ovulation starts in most people during puberty around age 13. During the first few years,
ovulation can be sporadic with an egg being released on some months but not others.
After those first few years, things settle down and most people will then release an egg
every month. There are times, however, when an egg will not be ovulated. For example, if
a person is taking a medication which suppresses ovulation, such as birth control pills, ovulation
will mostly not occur. Athletes, especially runners and dancers will also commonly stop
ovulating. Ovulation is also interrupted during a pregnancy or after while a person is nursing.
Menopause occurs when only a few dozen eggs remain in the ovaries. The average age of
menopause in the United States is about 50. No more eggs are released from the ovaries
after menopause. Ovulation is permanently stopped.
If you do the math, you will notice that the numbers do not make sense.
If a 26 week fetus has 2 million eggs and 1 egg is released every month from age 13 until age
50 when essentially all of the eggs are gone, that is only about 444 eggs! What happened to the rest?
The truth is that the vast majority of eggs are not lost due to ovulation, they are lost due to
degeneration. Doctors call this oocyte atresia. This process of losing eggs starts at about
20 weeks before birth. At the time of birth, only about 200,000 eggs remain in the ovaries.
During the ovulation years, one egg is typically released every month, but that egg comes from a
larger group of eggs called a cohort. The size of the cohort can be somewhere around 60 to
one hundred eggs. This large group of eggs starts to mature because of the hormones being produced
from the pituitary gland. Because of the changing hormone levels and the differing sensitivity of
the eggs to those hormones, some eggs will stop developing. Just before ovulation occurs, usually
only one egg is left which will then be released but the rest of that cohort will then degenerate.
Fertility medications work by changing the hormone dynamics
so that more than one egg will mature. In other words, the fertility medications are salvaging
some of the eggs that would otherwise have been lost due to degeneration.
The reverse is true for people that are not ovulating. The same number of eggs
will still degenerate during that time whether a person ovulates one egg or not.
This is why people who use birth control pills or
have several pregnancies still go through menopause at the same age as those who havent.
Fertility medications do not cause a person to run out of eggs faster. Does anything
else cause the number to drop more rapidly? Yes. There are several factors that accelerate
the rate of degeneration. The most common is cigarette smoking. Exposure of the ovaries
to chemotherapy or radiation can also accelerate the loss of eggs and of course
surgery to remove part or all of the ovary will also result in less eggs.
Our InfertilityTV Bottom Line is this. Do not worry. The use of
fertility medications will NOT cause you to run out of eggs any faster.