Center for Young Women's Health

Fertility Awareness Based Method (FAB) - formerly called "Natural Family Planning"



  • FAB stands for: Fertility Awareness-Based method which prevents pregnancy by not having intercourse on the days you are most fertile.
  • FAB is not a reliable method of birth control but it is more effective when condoms are also used.
  • It takes time and practice to know exactly when you're ovulating for this method to be most effective.

FAB is also known as natural family planning. Some women choose this method because of concerns about side effects from other contraceptive methods such as birth control pills. Others may use the FAB method of contraception for religious or cultural reasons. Whatever the reason, it takes a lot of practice to learn how to use this method correctly. Out of all the different methods of birth control, this method is the least effective in preventing pregnancy.


What are the fertility awareness-based (FAB) methods of contraception?

FAB methods are a way to become aware of the time when you ovulate so that you can prevent pregnancy. Couples who are trying to become pregnant can also use this method. When using this method to prevent pregnancy, sexual partners do not have sexual intercourse during ovulation. Ovulation is the time during a woman's menstrual cycle when she is most likely to become pregnant.


Out of 100 women using natural family planning
Typical use: 24 women become pregnant 24 Pregnant Women
Perfect use: Less than 1 to 5 (average 3) women become pregnant 5 Pregnant Women

How do you practice the fertility awareness-based methods?

First, you'll need to figure out when you are ovulating (when your ovaries release the egg each month). Women can get pregnant a few days before to a few days after ovulation. Sperm can live for up to 5 days and the egg lives 24 hours. So even if you are not ovulating the day you have sexual intercourse, you can still get pregnant if you start ovulating within 5 days because the sperm can still be alive. If you have finished ovulating and you have sex the next day, you can get pregnant since the egg can still be fertilized. To avoid pregnancy you should NOT have sexual intercourse a few days before and after the day that you ovulate. Keep in mind that ovulation may be tricky to predict because teens often have irregular cycles.


What are the different FAB methods?

You can use one method or a few methods to find out when you are ovulating. These methods include:


Once you figure out when you are ovulating, you should NOT have sexual intercourse during your fertile time. The fertility awareness-based methods can be tricky to figure out, but if you think using this method to prevent pregnancy is a good idea for you, talk to your health care provider.


How effective are the fertility awareness-based methods (FAB)?

If women use the FAB methods every time they have sexual intercourse and follow instructions perfectly every time (a woman has to figure out when she is ovulating and does not have sexual intercourse during this time), it is 95% effective. This means that if 100 women use the FAB methods all the time and always use them perfectly, and their cycles are always regular less than 3 to 5 women will become pregnant in a year.


Perfect use hardly ever happens and so this method is typically only 77% effective. This means that if 100 women use the FAB methods, 23 women will become pregnant in a year. Failure rates can be high using the FAB methods if you have irregular periods, which are more common in teens. The FAB methods do not protect against sexually transmitted infections- you must use condoms.


Are there any problems with the fertility awareness-based method (FAB)?

The FAB method is not the best type of contraception there is, but it is considered "natural" and many religions approve it. The good thing is that there are no side effects from the FAB method. However, the fertility awareness-based methods are not very reliable. Illness can change your body temperature and vaginal infections can cause changes in the mucus of your cervix. With these changes, there's a greater chance that you can get pregnant.


Written and reviewed by the CYWH Staff at Boston Children's Hospital


Updated: 9/24/2012


Related Guides:


There are many different types of contraception that vary in how effective they are at preventing pregnancy, how much they cost, how easy they are to use, and whether they also protect against STDs...


Making Healthy Sexual Decisions

You may be thinking about what it means to be involved in a sexual relationship. As a young adult, it's normal to think about sex, have sexual feelings, and have a desire to learn more about your own body...



Did you know that about 800,000 teen girls become pregnant in the United States each year, and more than 80% of these pregnancies are unplanned? Dealing with a pregnancy is one of the most important decisions a teen may need to make...

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