Birth Control: Rhythm Method (Fertility Awareness)


The rhythm method is a type of birth control. Sometimes referred to under the category of “natural family planning,” or NFP, this approach to birth control involves a woman monitoring when she is fertile and avoiding sexual activity, or using other types of birth control such as condoms, at that time of her cycle. The rhythm method is also called the fertility awareness method.

The rhythm method is not as effective at preventing pregnancy as other methods, such as taking birth control pills ‒ it is only effective about 76 percent of the time ‒ but it appeals to some women who do not like the side effects that are possible with other options. It is also appealing to women who have religious objections to using medical forms of birth control.

Birth Control 

How does the rhythm method work?

Women are only fertile (an egg is present) for a few days each month. Women using the rhythm method monitor their body and analyze their past menstrual cycles to try to determine when their fertile days are. They can then either choose to not have sex during those days, or can use a “barrier” form of birth control, such as condoms or spermicide.

There are several ways by which women can monitor their fertility. The most common approach used on the rhythm method involves knowing how long their cycles usually run, and then using that information to determine when they are fertile. The average menstrual cycle is 28 days but cycles of 21 to 35 days can still be considered “normal.” Some women will have the same number of days in their cycle each month, while others will see variation from month to month.

The rhythm method works best for women whose cycles are consistent because it is easier to predict when she ovulates (releases an egg from her ovaries).

Most women will have a period 14 to 16 days after ovulation, regardless of the length of their overall cycle. Counting backward from the day their period begins can be a good way to know when they ovulated. Although eggs are only available for fertilization for about 12 hours after being released from the ovaries, sperm can live in a women’s body for a few days, so it is advised that women using the rhythm method avoid sexual intercourse for three days before and after ovulation. The longer a woman keeps track of her cycle, the more clearly she will see a pattern, yielding more accurate information.

How can I track my fertility?

There are other methods to track fertility, besides using the calendar. These can include:

  • Cervical mucus: One way is for women to monitor their cervical mucus. The mucus changes during ovulation, becoming stretchy and clear. It is often compared to an uncooked egg white. Women using this method check their mucus daily and record what they find. Over time, they will likely see a pattern of when it changes, revealing their fertile times. The cervical mucus can be affected by many things, such as breastfeeding, taking birth control pills, having a sexually transmitted infection, or having had surgery on the cervix in the past, so this method can be misleading for some women.
  • Temperature: Another way to monitor fertility is for a woman to take her temperature first thing each morning (before even sitting up in bed) with a digital or mercury thermometer that measures basal body temperature. The thermometer needs to display a measurement that reads to the tenths place value. When a woman ovulates, her basal temperature will rise 0.5 to 1 degree. It is recommended that women avoid unprotected intercourse for the five days prior to a basal body temperature increase, as healthy cervical mucus can keep sperm alive for five to seven days. Women can resume intercourse 24 hours after they have the spike in basal body temperature because the egg only lives 12 to 24 hours. As a woman tracks her basal body temperature over time, and charts it on paper (there are many charts available free online), the patterns of her cycle can become clear and provide valuable insights into her body. For example, if she does want to become pregnant later in life, this information can help her time sex to maximize her chances.
  • Cervical changes: Checking the cervix for physical changes, including a softer texture, higher position, and increased opening can also be a sign of ovulation.
  • Combination: Using all three of these approaches can improve the effectiveness of natural family planning.

What is the biggest drawback to using the rhythm method?

The biggest drawback is that it is not as effective in preventing pregnancy as other methods of birth control.

Among 100 women in their first year of using the rhythm method, 24 will typically become pregnant. This is much higher than most other methods (see previous section).

What are the other downsides to the rhythm method?

It can be hard to be sure of the days you are most fertile, especially if you do not have regular periods. Women have to think about these issues every time they want to have sex, which many women find to be a burden.

Also, the rhythm method provides no protection against sexually transmitted diseases. It is best used in monogamous (both partners are only having sex with each other) relationships.

In addition, it can take several months of monitoring for you to have a clear pattern of when you are fertile. You may need to use barrier methods of birth control for at least the first few months.

The use of birth control medications can give some women relief from pain during and before their periods. Users of the rhythm method do not receive such benefits.

What are the benefits to using the rhythm method?

One benefit is that it is free and does not require you to go to a doctor annually to get a prescription refilled or get an implant replaced or monitored. Also, if you do decide you want to have a baby later, you can start trying right away. You don’t have to stop taking any medication or have anything removed. Since you will already likely have a very good idea about when you are fertile each month, you will be prepared to know the best timing for sex.

Another major benefit is that you avoid the possible side effects that can come with other methods, such as pills, patches, shots or implanted devices. While these side effects are minor for most women, they can include:

  • Bleeding between periods or missed periods
  • Weight gain
  • Changes in mood
  • Sore breasts
  • Headaches
  • Skin irritation
  • Nausea
  • Bone loss with long-term use
  • Pain or infection at the insertion site for implanted devices
  • Difficulty removing an implant later in life
  • Ovarian cysts
  • Increased blood pressure
  • Increased risk of blood clots, stroke and heart attack
  • Vaginal discharge or irritation
  • Allergic reactions
  • Permanent loss of fertility due to complications (rare)

What are my other options for birth control?

There are many options available today for birth control. These include:

Abstinence: Not having sex with a man is 100 percent effective at avoiding pregnancy.

Barrier methods: These stop the sperm from reaching the egg, and must be used each time you have sex. Options include condoms, spermicide, diaphragms, sponge, or cervical cap. Diaphragms are about 88 percent effective; condoms about 82 percent. Combining these methods increases their overall effectiveness.

Long-acting reversible contraceptives: These are birth control options that your physician inserts into your body, such as intrauterine devices (often called IUDs) and hormonal implants. They free you up from having to think about birth control for months or even years at a time, and can be removed if you want to become pregnant later in life. When used correctly, long-acting contraceptives are about 99 percent effective.

Short-acting hormone treatments: These are birth control options that you have to take or use daily (or monthly, or quarterly, in some cases), including birth control pills, a patch, a shot, or a vaginal ring. Shots are about 94 percent effective and the pill, the patch, and the ring are about 91 percent effective.

Sterilization: This means the person has a surgical or medical procedure that leaves him or her permanently unable to have children. These procedures include tubal ligation or occlusion for women, or a vasectomy for men. When these procedures are done correctly, they are nearly 100 percent effective.

The rhythm method is about 76 percent effective (see next section).

What if I realize I have made a mistake and had unprotected sex during my fertile time?

Emergency contraception medications are available in most drugstores today. Plan B One-Step® and generic versions do not require a prescription but some other types of emergency contraception do. All types work best if taken as soon as possible, but, depending on the type, may still be effective up to five days after having unprotected sex.

If you are going to be using the rhythm method as your primary source of birth control, you might want to ask your doctor ahead of time about the best emergency conception option for you if a problem arises. Since many women who use the rhythm method are doing so to avoid unwanted side effects of other birth control types, knowing ahead of time about the potential side effects of each of the types of emergency birth control will prepare you to make a good decision if the time comes.

How can I learn more about natural family planning methods?

There are professionals in most communities (often nurses) who can help you learn more about applying the rhythm method or other non-medical birth control methods to your life. Your gynecologist or primary care doctor may be able to recommend someone to you. The more you know about this approach to birth control, the better your results will be.

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