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The luteal phase, also referred to as
'days past ovulation' or 'DPO', is the portion of the cycle that begins at
ovulation and ends the day before your next period. It typically lasts about 14
days and does not usually vary by more than a day.
The process of ovulation is triggered by the release of Luteinizing Hormone
(LH).
The LH level increases significantly about 1-2 days before
ovulation, causing the egg to be released from the ovary (this increase is known
as the 'LH surge'). The egg travels down the fallopian tube towards the uterus.
If fertilization does not occur within 24 to 48 hours after ovulation, the egg
disintegrates and is expelled with the uterus lining at the start of your next
period, usually 12-16 days later. If fertilization occurs, the egg implants
itself in the lining of the uterus and begins its growth, resulting in a
pregnancy.
The luteal phase is named after the corpus luteum (Latin: "yellow
body"), a structure that grows on the surface of the ovary where a mature
egg was released at ovulation. The corpus luteum produces progesterone to
prepare the body for pregnancy. The luteal phase must be at least 10 days
long for implantation to occur and to support a pregnancy. A short luteal phase can
cause fertility problems making it difficult for a woman to get pregnant.
The length of the luteal phase determines the time of ovulation within your
menstrual cycle. Ovulation can be delayed by a number of factors, such as
stress, medication or increased activity, but the length of the luteal phase is
usually constant. Taking this into account, you can calculate the time of
ovulation within your cycle by subtracting the length of your luteal phase from
the length of your cycle. For example, if your cycle is 28 days long and your
luteal phase is 12 days long, ovulation will occur on day 16 of your cycle
(28-12=16).
The only way to determine the exact length of your luteal phase is through
hormone-specific blood tests, however fertility
charting can help you to determine the length of your luteal phase with a
good degree of accuracy.
If you are not sure about the length of your luteal phase, you can assume it
is 14 days as that is the average length for most women.
Since a woman's luteal phase is very consistent,
the length of your luteal phase is a very good way to identify if you've
succeeded in conceiving. For
example, if your luteal phase is usually 12 days and never more than 13 days, you
are currently at day 15 of your luteal phase and your menstrual period has not
yet arrived, this
is a very good indicator that pregnancy has occurred.
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