How Pregnancy Occurs
The first thing in preventing pregnancy, is understanding the woman’s ovulation cycle and how pregnancy occurs.
A woman’s menstrual cycle and ovulation time (also called her fertile time) has everything to do with achieving
pregnancy and avoiding pregnancy.
What is Ovulation?
Ovulation occurs when a mature egg is released from the ovary, pushed down the fallopian tube and is available
to be fertilized. The lining of the uterus has thickened to prepare for a fertilized egg. If no conception occurs,
the uterine lining as well as blood will be shed. The shedding of an unfertilized egg and the uterine wall is the
time of menstruation.
Key Facts of Ovulation:
An egg lives 12-24 hours after leaving the ovary
Normally only one egg is released each time of ovulation
Ovulation can be affected by stress, illness or disruption of normal routines
Some women may experience some light blood spotting during ovulation
Implantation of a fertilized egg normally takes place 6-12 days after ovulation
Each woman is born with millions of immature eggs that are awaiting ovulation to begin
A menstrual period can occur even if ovulation has not occurred
Ovulation can occur even if a menstrual period has not occurred
Some women can feel a bit of pain or aching, near the ovaries during ovulation called
mittelschmerz which means "middle pain" in German
If an egg is not fertilized, it disintegrates and is absorbed into the uterine lining
A woman's monthly cycle is measured from the first day of her menstrual period until the first day of her next
period. On average, a woman's cycle normally is between 28-32 days, but some women may have much shorter cycles or
much longer ones. Ovulation can be calculated by starting with the day the last menstrual period (LMP) starts or by
calculating 12-16 days from the next expected period. Most women ovulate anywhere between Day 11 - Day 21 of their
cycle, counting from the first day of the LMP. This is what many refer to as the "fertile time" of a woman's cycle,
because sexual intercourse during this time increases the chance of pregnancy. Ovulation can occur at various times
during a cycle, and may occur on a different day each month.
The Ovulation Cycle divided into two parts:
The first part of the ovulation cycle is called the follicular phase. This phase starts the first day of the
last menstrual period (LMP) and continues until ovulation. This first half of the cycle can differ greatly for each
woman lasting anywhere from 7 days until 40 days. The second half of the cycle is called the luteal phase and is
from the day of ovulation until the next period begins. The luteal phase has a more precise timeline and usually is
only 12-16 days from the day of ovulation. This ultimately means that the day of ovulation will determine how long
your cycle is. This also means that outside factors like stress, illness, and disruption of normal routine can
throw off your ovulation which then results in changing the time your period will come. So the old thought that
stress can affect your period is only partly true. Stress can affect your ovulation which ultimately determines
when your period will come, but stress around the time of an expected period will not make it late—it was already
determined when it would come 12-16 days earlier!
Fertility Awareness is one way to track when ovulation occurs and it includes studying the changes in cervical
mucus and using a basal thermometer. Cervical fluid will change to a wet, slippery substance that resembles "egg
whites" just before ovulation occurs and until ovulation is over. A basal thermometer helps track a body
temperature rise, which signals that ovulation has just occurred.
Another way to track ovulation is through ovulation kits and fertility monitors. Tracking ovulation can help a
woman get a better idea of when pregnancy can and can not occur during her monthly cycle. Once ovulation has
occurred, there is nothing you can do to increase your chances of pregnancy. Your next step is to begin watching
for early pregnancy symptoms.
View and print an Ovulation Calendar, or use our Ovulation Calculator, to better understand your menstruation
cycle and ovulation.
From the Menstrual Period to Ovulation (the details you may not know!)
When your menstrual cycle begins, your estrogen levels are low. Your hypothalamus (which is in charge of
maintaining your hormone levels) sends out a message to your pituitary gland which then sends out the follicle
stimulating hormone (FSH). This FSH triggers a few of your follicles to develop into mature eggs. One of these will
develop into the dominant follicle, which will release a mature egg and the others will disintegrate. As the
follicles mature they send out another hormone, estrogen. The high levels of estrogen will tell the hypothalamus
and pituitary gland that there is a mature egg.
A luteinizing hormone (LH) is then released; referred to as your LH surge. The LH surge cause’s the egg to burst
through the ovary wall within 24-36 hours and begin its journey down the fallopian tube for fertilization. The
follicle from which the egg was released is called the corpus luteum and it will release progesterone that helps
thicken and prepare the uterine lining for implantation. The corpus luteum will produce progesterone for about
12-16 days (the luteal phase of your cycle.) If an egg is fertilized, the corpus luteum will continue to produce
progesterone for a developing pregnancy until the placenta takes over. If fertilization does not occur the egg
dissolves after 24 hours.
At this time your hormone levels will decrease and your uterine lining will begin to shed about 12-16 days from
ovulation. This is menstruation (menstrual period) and brings us back to day 1 of your cycle. The journey then
begins all over again.
The time of ovulation is one of the most important things a woman should understand about her body since it is
the determining factor in getting pregnant and preventing pregnancy. The process can be confusing and somewhat
overwhelming when trying to understand. There are many frequently asked questions about the ovulation process and
the Association has attempted to address those for you. If you still have further questions regarding ovulation, we
encourage you to either talk with your health care provider or contact the American Pregnancy Association for more
information. Being informed on what your body does, can help you feel more in charge of your health.