How do you know when you're most fertile?

It's kind of funny: many of us spend years trying not to get pregnant, and then when we do want to have a baby, it may be harder than we thought. If you're trying to get pregnant, the first thing you need to know is when you are ovulating. Ovulation is when the ovary develops an egg and releases it to travel through the fallopian tube to the uterus, where it can be fertilized by sperm and begin the process of becoming an embryo. So learning when you ovulate and having sex then is a good way to increase your chances of getting pregnant in a particular month. But how do you know when you're ovulating? There are a few ways to figure it out.

Calculating your fertile time

The least high-tech way is a reverse of the rhythm method (also called natural family planning) of birth control. In this method, you track your menstrual cycle to figure out which days you are most fertile. Day one of your menstrual cycle is the first day of your menstrual blood flow. Your fertile days are most likely from day 10 through day 17 of the cycle. If your average cycle length is different from the standard 28-day cycle then the fertile time must be adjusted to the length of your average cycle. For instance, if your cycles range between 26 to 30 days, then your fertile time would be from day 8 through day 19.

To determine this apply the following formula:

· Subtract two days from day 10 of the 28-day cycle: 10-2=8

· Add two days to day 17 of the 28-day cycle: 17+2=19

For example, if your cycles range between 25 and 31 days, then:

· Subtract three days from day 10 of the 28-day cycle: 10-3=7

· Add three days to day 17 of the 28 day cycle: 17+3=20

Your fertile time will be days 7 thru 20 of your menstrual cycle. Remember, day one of your cycle is the first day of your menstrual flow. By marking the fertile days of your cycle on your calendar each month, you can know in advance when to have intercourse.

Another approach involves a slightly different calculation:

· Subtract 18 days from your shortest cycle length, and subtract 11 days from your longest cycle length.

The result will define your fertile time. For example, if your shortest cycle is 22 days (22-18=4) and your longest cycle is 27 days (27-11=16) then your fertile time will be cycle days 4 to 16.

Because menstrual-cycle lengths vary from person to person, and often from month to month in the same woman, you cannot assume your fertile days will be exactly the same days every month. By keeping track of your menstrual cycle for at least eight months before relying on this method, you will be more certain about your average cycle length and how much it varies.

You can also tell that you are ovulating by looking for signs within your body. One is that a woman's cervical fluid will change to a wet, slippery substance (some people say it resembles egg whites) just before ovulation occurs. It will remain this way until ovulation is over. Your temperature will also rise slightly when ovulation has just occurred.

Ovulation detection kits

The level of a hormone called luteinizing hormone (LH) increases dramatically as ovulation approaches. Ovulation detection kits test for the LH in your urine. The test is positive when LH levels are high enough to trigger ovulation.

Studies show that ovulation detection kits are reliable but cannot tell you the exact moment when you will ovulate. Prices of these kits vary between $25 and $35, so it can get expensive to use these month after month.

Once you figure out when you're ovulating, then you can let the romance begin!

Are you trying to figure out when you are ovulating? How are you going about it?

Kristen Eckler, M.D., is an Instructor of Obstetrics, Gynecology, and Reproductive Biology at Harvard Medical School, and an Assistant Professor of Obstetrics, Gynecology, and Reproductive Biology at Massachusetts General Hospital.

The Fertility Diet
For many couples struggling with infertility, the best hope for having a baby often comes from expensive high-tech medical procedures coupled with sometimes unpleasant drugs. Now there's a safer, natural, and virtually free way to improve fertility that's available to all couples: ten simple changes in diet and lifestyle. From Harvard Medical School, The Fertility Diet offers a plan that not only improves ovulation and fertility, but also offers a healthy start to a pregnancy and is good for the heart, bones, and the rest of the body throughout pregnancy and beyond.

Are you trying to conceive or are you in the beginning stages of pregnancy? Do you feel excited, daunted or confused? Join Moms2B, a group to learn about prenatal care and share your pregnancy "firsts" each step of the way. To join, click here.