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

Tracking Ovulation:

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.