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What is ovulation?
Ovulation is the release of an egg from a woman’s ovaries and
is essential for getting pregnant. Ovulation is spontaneously
triggered about 36-40 hours after blood levels of a hormone
called luteinizing hormone (LH) rise. This is called the LH
surge. Once released from the ovary, the egg is picked up
by and travels down the fallopian tube where it can meet
sperm to become fertilized.
Why is ovulation important?
A problem with ovulation is a common cause for infertility. For
a couple who is trying to achieve pregnancy, knowing when
the woman is about to ovulate can be particularly helpful in
planning when to have sex. If a woman is trying to find the
reason she is not getting pregnant, it is helpful to know if she
is ovulating. Having regular menstrual periods between 21
and 35 days in length accompanied by menstrual cramps
is a good indication of ovulation. There are several ways
to test for ovulation, including: the basal body temperature
(BBT) chart, urine test kits to measure LH levels, blood tests
to measure levels of certain hormones and transvaginal
What tests are available to check for ovulation?
Blood tests to measure hormone levels
Estradiol (a type of the hormone estrogen) is produced by
the follicle as it grows and levels go up quickly just before
ovulation. If fertility medicines are being used to cause a
woman to ovulate, estradiol levels are checked more often to
keep an eye on the growth of the follicle, but it is not used to
tell you when you might ovulate.
A rise in LH levels in the blood can predict when the follicle
(sac where the egg ripens) is ripe and ready for ovulation.
Because LH is released in pulses or short bursts, the LH
surge is not always found by a single blood or urine test.
Increased progesterone levels in the blood a week before the
menstrual period usually indicates ovulation has occurred
but cannot predict when it will occur.
Urine test kits to measure luteinizing hormone (LH)
These home test kits are available at drug stores and show
changes in the level of LH in a woman’s urine. Since LH
hormone builds up in the urine, once it is detected in the
urine, ovulation usually takes place within 12 to 24 hours
(usually about 14 days before the start of a woman’s
menstrual period). For women with irregular periods, urine
testing should be timed according to the earliest and latest
possible dates one is expected to ovulate. Urine testing for
LH surge should begin at least 2 days before the expected
day of ovulation and continue until the LH surge or through
There is an 80% chance of detecting ovulation with 5 days
of testing, and a 95% chance with 10 days of testing. Once
an LH surge is documented, it is no longer necessary to
continue testing during that cycle. Occasionally, ovulation
may not occur in a cycle despite an LH surge. If ovulation
is not detected in 2 or more cycles in a row, there may be a
problem with ovulation and you should discuss this with your
Some fertility test kits check for both LH and estrogen in the
urine. This does not necessarily increase your chances of
pregnancy and should not be used if you are taking medicines
to help you ovulate.
The egg develops within a part of the ovary called the
follicle (a fluid filled sac). As the egg gets ready to ovulate
the follicle grows larger. Follicle growth can be measured
with ultrasound, a technique which uses sound waves to
produce an image on a monitor screen using a tampon-like
probe placed in the vagina. Before ovulation, the follicle is
thin-walled and filled with fluid. Ovulation generally happens
when the follicle measures between 1.8 and 2.5 centimeters.
For women having treatment for fertility, ultrasound may help
time intercourse or insemination. In women taking fertility
drugs, ultrasound may be done on several different days
during the menstrual cycle to measure and monitor each
Basal body temperature (BBT) chart
Daily measurement of basal body temperature can help
determine if ovulation has occurred. However, BBT charting
is only an estimate of ovulation timing and can confirm that
ovulation has happened but will not predict when it might occur.
Although not very helpful or accurate to time intercourse, it
is an inexpensive, easy way to gather information at home.
Although determining if and when ovulation is occurring might
seem frustrating and time consuming, it is often an essential
step toward achieving pregnancy. It is important that women
work with their healthcare providers to decide which method
of ovulation detection is best for them. If these tests indicate
that the woman is not ovulating, or that she has irregular
cycles, treatments are available to correct the problem and
increase the chances of a successful pregnancy.