Detecting ovulation

What is ovulation?
Ovulation is when one or more eggs are released from the ovary and is the fertile time of your menstrual cycle. Each month, many eggs mature inside the ovary. The largest is expelled into the pelvic cavity and swept into the Fallopian tube. Which ovary releases the egg is fairly arbitrary. Ovulation does not necessarily rotate between ovaries each cycle.

How does ovulation determine when I can get pregnant?
To be fruitful and multiply, you must have sexual intercourse during the period spanning four or five days before ovulation to about 24 hours afterward. The reason: Sperm cells can live for four or five days, but an egg survives no more than 24 hours after ovulation. Unless, of course, fertilization occurs.

If you have sex near the time of ovulation it stands to reason you'll increase your chances of getting pregnant. And you'll be happy to know that the odds are with you: In normally fertile couples there is a 25 percent chance of getting pregnant each cycle, meaning around 75 to 85 percent of women who have sex without using birth control will get pregnant within one year. You can try to up your likelihood of getting pregnant by learning to pinpoint exactly when you ovulate by familiarizing yourself with the cyclic hormonal and physical changes that take place in your body each month. You can also use this knowledge to attempt birth control by avoiding intercourse near the time of ovulation.

How can I tell when I'm ovulating and therefore most fertile?
Figure out when your next period is due to begin and count back 12 to 16 days. This will give you a range of days when you will probably be ovulating (for women with a 28-day cycle, the 14th day is often the one). To use this method, you must know how long your cycle usually lasts. Try BabyCenter's ovulation calculator if you want us to do the math for you.

The best way to determine your most fertile time, though, is to pay attention to your body and learn to spot the signs that ovulation is imminent.

Change in cervical mucus. As your cycle progresses, your cervical mucus increases in volume and changes texture. The greater volume and changes in texture reflect your body's rising levels of estrogen. You are considered most fertile when the mucus becomes clear, slippery, and stretchy. Many women compare mucus at this stage to raw egg whites.

The role of mucus is to nourish, protect, and speed the sperm on its way up through the uterus and into the Fallopian tubes for the rendezvous with your egg.

A rise in body temperature. Following ovulation, your temperature can increase by 0.5 to 1.6 degrees. You won't feel the shift, but you can detect it by using a basal body temperature (BBT) thermometer. This temperature spike indicates that you've ovulated (releasing an egg stimulates the production of the hormone progesterone which raises body temperature).

You're most fertile in the two or three days before your temperature hits its high point. A few experts think you may have an additional 12 to 24 hour window of fertility after you first notice the temperature creep up, but most say at that point it's too late to make a baby. "It can take one to two days after ovulation for progesterone to build up enough to raise your body temperature. But since the egg can only survive for about 24 hours, at that point it's too late for fertilization," says Tracy Telles, an obstetrician at Stanford University in Palo Alto, California. That's why experts recommend that you chart your temperature (taken each morning) for a few months to detect a pattern and pinpoint your likely ovulatory date. Then you can plan to have sex during the two to three days preceeding the day your temperature normally rises.

Lower abdominal discomfort. About one-fifth of women actually feel ovulatory activity, which can range from mild achiness to twinges of pain. The condition, called mittelschmerz, may last anywhere from a few minutes to a few hours.

How do ovulation predictor kits work?
Available at drugstores and grocery stores without a prescription, ovulation predictor kits detect the surge in luteinizing hormone (LH) just before ovulation. They're easier to use and often more accurate than the BBT method and they can predict ovulation 24 to 36 hours in advance and help you maximize your chance of conception the very first month you use them.

But they're not foolproof. They can measure LH (you get either a positive or a negative result, not a number), but can't indicate whether you ovulate after a positive response; LH can surge with or without the release of an egg. False LH surges can also take place before the real one.

For maximum accuracy, follow the kit's directions to the letter. (However, if the instructions say to test your first urine of the day, you may want to test your second catch instead. Your urine can become concentrated overnight and might give you a false-positive result.) Your cycle starts on the first day you have your period. If you have a 28-day cycle, start the test on day 11 and use it for six days (or however many days the manufacturer recommends). If your cycle is longer, say 35 days, start on day 14 and test for nine days. If you have an irregular cycle, you may find that this is the least satisfying way for you to detect your ovulation because you'll have to buy many kits to use over a long period of time. If your cycle runs between 28 and 40 days, your ovulation may range between days 14 and 26. Because the kits (which range in price from $20 to $50) usually provide only five to nine days' worth of tests, you'll need to buy at least two kits a month.