Premature Ovarian Failure (POF)
What is premature ovarian failure (POF)?
Health care providers use the term premature ovarian failure to describe a stop in normal
functioning of the ovaries in a woman under the age of 40. Many women naturally
experience a decline in fertility at age 40; this age may also mark the
beginning of irregularities in their
menstrual cycles that
signal the onset of menopause. For women with
premature ovarian failure, the fertility decline and menstrual
irregularities occur before age 40, sometimes even in the teens. Some health
care providers also use the term primary ovarian insufficiency to describe this
condition.
In the past, health care providers called this condition premature menopause,
but this term is not an accurate description of what happens in a woman with
premature ovarian failure. A woman who has gone through
natural menopause will rarely ever have
another period; a woman with premature ovarian failure is much more likely to have periods, even
though they might not come regularly. There is virtually no chance for a woman
who has gone through menopause naturally to get pregnant; in some cases, a woman
with premature ovarian failure can still get pregnant.
What causes premature ovarian failure?
Although researchers have a general idea of what causes premature ovarian
failure, in most cases
the exact cause remains unclear.
To understand what happens in premature ovarian failure, you need to understand what happens in a
woman's body when it's functioning normally.
The Normal Menstrual Cycle
In general, a woman's reproductive health involves her:
- Hypothalamus (pronounced high-poe-THAL-amus)
- part of the
brain that functions
as the main control for the body's
reproductive system.
The hypothalamus works like a thermostat in a furnace, in that it controls the levels of different
hormones and other chemicals in the body. If the hypothalamus detects that there
is too little of a hormone in
the body, it orders the body to make more.
- Pituitary (pronounced
pitt-OO-ih-terry) gland - the body's master gland. The
pituitary sends out hormones, or chemical signals to control the other glands in
the body. The pituitary gets orders from the hypothalamus about what the body
needs.
- Ovaries - the source of eggs in a woman's body. The ovaries have follicles,
which are tiny, fluid-filled sacs that hold the eggs. The ovaries also make
hormones that help to maintain a woman's health, such as
estrogen,
progesterone,
and testosterone. The ovaries receive the chemical signals from the pituitary
and respond by making certain hormones. In premature ovarian failure, the ovaries stop working
correctly in both their egg production role, and in their hormone production
role.
- Uterus - where a woman carries a baby, also called the "womb." The
uterus has
different layers; its innermost layer or lining is called the endometrium - endo
means "inside" and metrium (pronounced MEE-tree-um) means "womb." The
endometrium functions as a bed for an
embryo when a woman is
pregnant. If no pregnancy occurs during the cycle, then the endometrium is shed as a menstrual
flow, or a period, and the cycle starts all over again.
Picture of the female reproductive system
These parts interact with one another to coordinate a woman's monthly
menstrual cycle.
- The hypothalamus keeps track of the level of
estradiol (pronounced
ess-trah-DYE-awl) in the body. Estradiol is the natural estrogen that a woman's
body makes, so we'll call it estrogen from now on.
- When the level gets low, the hypothalamus sends an order to the pituitary
gland telling it that the body needs more estrogen.
- The pituitary gets the order and responds by sending out follicle stimulating
hormone (FSH), a hormone that causes the follicles on the
ovary to grow and
mature. Mature follicles make estrogen and other substances, such as
inhibin.
The pituitary continues to make FSH until the mature ovarian follicles make
enough estrogen. If the follicles don't make enough estrogen, the level of FSH
goes even higher.
- When the level of estrogen gets high enough, the hypothalamus and pituitary
know that there is a mature egg in one of the follicles. To get this egg to the
uterus so that it can be fertilized, the pituitary sends out a large burst of
luteinizing hormone (LH). LH breaks open the mature follicle to release the egg,
which allows it to move toward the uterus. The level of LH is only high during
the time an egg is being released. This LH burst is the basis for home
ovulation
detection kits. Because LH may be high throughout much of the menstrual cycle in
women who have premature ovarian failure, home ovulation detection kits are unreliable in these women.
- The empty follicle is then transformed into a yellowish,
corpus luteum
(pronounced CORE-puss loo-tee-um). Corpus means "body" and luteum means "yellow." The corpus luteum makes progesterone, the hormone that prepares the
uterus for pregnancy.
- Increased levels of progesterone cause the endometrium to change in
preparation for pregnancy, should it occur. Once the endometrium is properly
prepared, it can support an embryo and allow the embryo to grow.
- If the egg is fertilized, it sends out a hormone called
HCG to let the body
know that it's there. HCG causes the corpus luteum to continue to make
progesterone, the hormone needed for pregnancy. Pregnancy tests measure the
level of HCG. If HCG is present, then it's likely that a woman is pregnant.
- If there is no signal, that is, no HCG is present because the egg wasn't
fertilized, the corpus luteum stops making progesterone. Without progesterone,
the endometrium starts to break down, and the woman's body sheds it as her
period.
Next: What happens differently in premature ovarian failure? »
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