How the rhythm method of birth control works

What is fertility awareness?

The fertility awareness method (FAM) is a type of natural family planning where you learn how to track your menstrual cycles, so you'll know when you're most likely to be fertile. You can use FAM to improve your chances of conceiving, or to prevent a pregnancy.

If you want to get pregnant, you can use FAM to figure out the best days to have sex. If you don't want to get pregnant, you can avoid having sex during your most fertile days, or use a barrier birth control method like the condom, female condom, diaphragm, or cervical cap.

These are a few of the techniques you can use to predict when you'll ovulate. Many women use more than one of these to improve the effectiveness of this method:

Calendar-based or rhythm method: You count the days in your menstrual cycle on a calendar or app to predict when you'll ovulate and estimate your most fertile window. In a variation of the calendar-based method called the standard days method, days eight to 19 of your cycle are when you're most fertile. If the time between your periods typically varies by more than a few days, using a calendar alone can lead to unintended pregnancies or frustration when trying to conceive.

Cervical mucus method: Cervical mucus is the fluid your cervix produces. The amount, texture, and appearance of this fluid changes at various times during your cycle. Right before ovulation, the amount of cervical mucus increases. It becomes clear, slippery, and thin to help the sperm swim to the egg. After ovulation, it decreases and gets thicker. Having sex every day or every other day while your mucus is thin and slippery can help you conceive.

TwoDay method: In this variation of the cervical mucus method, you ask yourself, "Did I notice any mucus today?" and "Did I notice any mucus yesterday?" If the answer to either or both of these questions is "yes," you're in the fertile zone.

Basal body temperature (BBT) method: Your basal body temperature is your temperature while you're at rest. It rises slightly – by 0.5 to 1 degree Fahrenheit – after you ovulate. To determine your BBT, take your temperature at around the same time each morning before you get out of bed. You're most fertile two to three days before your temperature rises.

Symptothermal method: Because FAM isn't as effective as other available methods in helping to achieve a pregnancy or prevent one, this approach combines two or three methods to increase accuracy. The most common combination is BBT plus cervical mucus tracking.

Lactational amenorrhea method (LAM): The lactational amenorrhea method (LAM) is based on the idea that milk production (lactation) makes your periods stop (amenorrhea). Exclusively breastfeeding usually delays the return of your fertility, so you may not have a menstrual cycle for some time after you give birth. Depending on how often you're nursing and your body’s reaction to it, it can take anywhere from a few months to more than a year to start ovulating again. That means you're less likely to get pregnant while you nurse – but because it's not impossible, you're safest using a back-up birth control method. Remember that you will ovulate two weeks before you get that first post-baby period, so waiting to start birth control until you get a period can lead to an unintended pregnancy with that first ovulation.

What is the rhythm method?

The rhythm method is another name for the calendar-based method of natural family planning. By using this specific type of natural family planning, you track your menstrual cycles over time to figure out when you ovulate and are most fertile.

By using the rhythm method, you can find your optimal times to conceive. Depending on whether you're trying to get pregnant or avoid a pregnancy, you can either plan sex for your most fertile days or use a barrier method of contraception to avoid an unintended pregnancy.

You might prefer the rhythm method because you want a more natural approach to family planning. Some women choose it because their religion is opposed to other birth control methods. In fact, the name comes from a 1932 book, The Rhythm of Sterility and Fertility in Women. The book's author, Dr. Leo J. Latz, was a proponent of this method because it aligned with the teachings of the Roman Catholic church.

How does the rhythm method work?

To start, you figure out the length of your menstrual cycle. A cycle can run anywhere from 21 to 35 days, but 28 days is the average. To measure out one cycle, count from the first day of your period to the first day of your next period. Following your cycles for at least six months before you start using this method will ensure you get an accurate count.

Find your shortest menstrual cycle. Subtract 18 from the total number of days. If your shortest cycle was 28 days long and you subtract 18, you'll get 10. That means the 10th day of your cycle is your first fertile day.

Now find your longest cycle and subtract 11 from the total number of days. If your longest cycle was 30 days and you subtract 11, you'll get 19. Your 19th day is your last fertile day.

If you're trying to get pregnant, have sex often during your fertile days. If you're trying to prevent pregnancy, avoid sex or use a barrier method during those days.

How effective is the rhythm method?

The rhythm method and other fertility awareness methods can be effective when you use them correctly. But because these methods require a lot of attention and regular menstrual cycles, their actual effectiveness tends to be much lower.

According to the American College of Obstetrician and Gynecologists, fertility awareness methods are 95 to 99 percent effective when used perfectly. But they're only 76 to 88 percent effective as they're typically used. That means out of 100 women who use these methods for contraception, 12 to 24 will get pregnant during the first year of use.

The effectiveness of any method depends on three factors:

• How accurately you can identify your fertile time
• How well you understand the method and can use it to identify your fertile days
• How consistently you use a barrier method or don't have sex on your fertile days

These methods can be tricky to use in certain situations. You might need extra help with them if:

• You have irregular periods.
• You recently had a baby and your menstrual cycles aren't yet regular.
• You are close to menopause.
• You just went off a hormonal birth control method like the pill.

Learning how to use the rhythm method and other fertility awareness methods can take some time. If you're interested in learning more, you and your partner can take a class or work with a trained counselor. You can always ask your healthcare provider or county health department how to find a teacher.

What are the pros and cons of the rhythm method?

The rhythm method has its pluses and minuses.

Some of the pros of using this method are:

• It's inexpensive or free to use.
• You have the chance to learn about your menstrual cycle.
• You don't have to take medication or use a device for birth control.

Some of the cons of using the rhythm method for contraception are:

• It's not as effective as any of the hormonal birth control methods or the non-hormonal IUD at preventing pregnancy.
• It won't protect you against HIV, gonorrhea, chlamydia, or any other sexually transmitted infections (STIs).
• You have to pay close attention to your menstrual cycles, mucus, and temperature or it won't be as effective.
• It may not work if you have irregular menstrual cycles.
• It can take the spontaneity out of sex.

Talk about the rhythm method with your partner to see if it's right for your family. You might also want to get advice from your healthcare provider.