Detecting Ovulation

What is ovulation?

Ovulation is the fertile time of your menstrual cycle, which occurs when a mature egg — or ovum — is released from one of your ovaries. After the egg is released, it travels down the fallopian tube, where it can be fertilized if sperm are present.

How do I know when I’m ovulating?

It can be tricky to figure out when you’re ovulating and even trickier knowing how to time intercourse. Your peak fertile time occurs during the two or three days immediately before ovulation, but fertilization can occur up to 12 to 24 hours afterward. Sperm can live in a woman’s body for as long as five days, but an egg will last no longer than 24 hours, so the timing of intercourse or insemination has to be as precise as possible.

Although you have two ovaries, ovulation does not necessarily alternate back and forth between them each cycle. Furthermore, scientists have recently come to believe that in the event that one of the fallopian tubes is blocked, the other tube’s fingerlike tentacles — which whisk the ovum into the tubes — can actually “walk” to the other side and grab an egg from the other fallopian tube.

There are several ways to know when to try to get pregnant: Pay close attention to the changes in your body for several months by recording your period cycles, documenting your temperature every morning with a special thermometer, using a commercial fertility monitor or ovulation predictor kit, or monitoring the texture of your cervical mucus. In general, if your cycles are regular, it’s easier to predict fertility time intervals.

For a rough idea of when you ovulate, figure out when your next period is due to begin, and then count back 12 to 15 days.

Calendar method

If you have a written record of your menstrual cycles over eight to 12 months, you can roughly estimate your fertile period. To find out your first day of fertility, subtract 18 from the number of days in your shortest cycle. When your next period begins, take this new number and count ahead that many days. This will be a reasonable guess for the start of your fertile days. Although this is an easy exercise, it is often unreliable for predicting fertility, especially if you have irregular cycles. Factors such as illness and stress can affect the timing of ovulation from month to month.

Changes in cervical mucus

Cervical mucus offers many women their best clue: As your estrogen level rises before ovulation, you may notice your natural discharge becoming whitish-clear and sticky, with a consistency like raw egg white. According to the American Academy of Family Physicians (AAFP), as many as two out of three couples who don’t have fertility problems will conceive if they have sexual intercourse on the days that the cervical mucus is clearest and most stretchy.

Basal body temperature

You can also try charting your basal body temperature (your body’s temperature when you’re at rest) using a special thermometer. This has long been used as a traditional measure of fertility, because your temperature can increase by about 0.5 to 1 degrees following ovulation.

However, because the temperature jump occurs after you’ve already ovulated and your peak fertile time occurs prior to ovulation, this method does not give you an advance prediction of when you are going to be most fertile. And in addition to the inconvenience of having to take your temperature every morning at the same time, the temperature changes are very subtle and can be difficult to interpret, especially if infertility might be a factor. Many women, however, have found it helpful to follow their temperature through several cycles in order to make an educated guess about when it’s going to spike in the future.

Ovulation predictor kits and fertility monitors

kits work by detecting a surge in the production of luteinizing hormone (LH) in your urine. Women’s levels of LH rise about 16 to 48 hours before ovulation, so the theory is that you’re most fertile shortly after that.

The downside is that these kits don’t tell you whether an egg was released or whether your cervical mucus was conducive to fertility. And they will be much less reliable if you are taking fertility drugs or if you are over 40. In recent years, a new device for predicting ovulation called a fertility monitor has become available in many retail stores. The monitor works by analyzing urine samples and identifying days of low, high, and peak fertility. Scientists are still studying its effectiveness, but results thus far have been encouraging. If your cycle is longer than 42 days or shorter than 21, this monitor may not be helpful.


You may also notice a crampy abdominal pain; for some women it’s a sharp twinge; others feel it as a dull ache. Known as mittelschmerz, this signals the moment the egg erupts from the ovary. The pain is believed to be caused by fluid, possibly blood, released from the ovary that irritates the abdominal lining. It can last anywhere from a few minutes to a few hours. Abdominal discomfort, however, is an extremely unreliable predictor of fertility because the pain often comes after ovulation, and you are trying to identify the period just before it.

Talk to your doctor about which of the above methods for detecting ovulation will work best for you. For a more complete picture of your fertility, you may want to use more than one method.

Am I most likely to get pregnant while I’m ovulating?

Yes and no. The best strategy, some experts say, is to have sex multiple times for the six days leading up to and including the day of ovulation. The reason: although sperm can live in your body for three to six days, an egg is able to be fertilized for only 12 to 24 hours after ovulation. A University of Utah study found that a woman is most likely to become pregnant if intercourse occurs one to two days before ovulation rather than on the actual day of ovulation, as popularly believed.

What are my chances of getting pregnant in any given cycle?

As long as you’re relatively young and don’t have an undiscovered fertility problem, the odds are pretty good. Fertile women under 30 who have sex during the ovulation period have a 20 percent chance of getting pregnant each cycle. The odds get worse as you age, however; women over 40 have only a 5 percent chance in any given cycle.


American Society for Reproductive Medicine. Ovulation Drugs.

National Women’s Health Information Center. Fertility Awareness and Infertility.

American Pregnancy Association. Ovulation Kits & Fertility Monitors. March 2005.

Mayo Clinic. How to Get Pregnant. April 18, 2009.

Stanford JB et al. Timing intercourse to achieve pregnancy: Current evidence. Obstetrics and Gynecology. December 2002, Vol. 100 No. 6:1333-1341.

University of California San Francisco Center for Reproductive Health. The Menstrual Cycle: Female Anatomy and Physiology. 2005.

American Academy of Family Physicians. Natural Family Planning. July 2010.

The Cleveland Clinic. Mittelschmerz (Painful Ovulation). Jan. 2007.

American Pregnancy Association. Ovulation: Frequently Asked Questions. Jan. 2005.

American Society for Reproductive Medicine. Age and Fertility. 2003.

American Pregnancy Association. Fertility Awareness: Natural Family Planning (NFP). Aug. 2005.

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