FAQ024, July 2014

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Fertility Awareness: Rhythm Method, Basal Body Temperature Method, and More

What is natural family planning?

Natural family planning is a form of birth control that is based on the timing of sex during a woman’s menstrual cycle. It is not a single method but a variety of methods.

What factors influence the success or failure of natural family planning methods?

The success or failure of any of these methods will depend on your ability to

  • recognize the signs that ovulation (the release of an egg from the woman’s ovary) is about to occur
  • not have sex during the fertile period or use another method, such as condoms, during the fertile period

How effective is it in preventing pregnancy?

Natural family planning is not as effective as most other methods of birth control. One in four women who use this method become pregnant. The method is not suited for the following women:

  • Women who should not get pregnant because of medical reasons
  • Women with irregular menstrual periods who may not be able to tell when they are fertile
  • Women with abnormal bleeding, vaginitis, or cervicitis (these make the cervical mucus method unreliable)
  • Women who use certain medications (for instance, antibiotics, thyroid medications, and antihistamines) that may change the nature of vaginal secretions, making mucus signs impossible to read
  • Women with certain problems unrelated to fertility (for instance, fever) that can cause changes in basal body temperature

When is ovulation likely to occur?

For most women, an egg is released almost 2 weeks before her next expected menstrual period. The egg remains able to be fertilized for about 24 hours after it is released. Sperm can live in a woman’s body for 3 days or more.

What are the types of natural family planning?

There are five methods of natural family planning:

1. Basal body temperature method

2. Ovulation/cervical mucus method

3. Symptothermal method

4. Calendar method

5. Lactational amenorrhea

What is the basal body temperature method?

The temperature method of natural family planning is based on the fact that most women have a slight increase in their normal body temperature just after ovulation. A woman using this method takes her temperature every morning before getting out of bed. She then records it on a graph. In this way, she is able to detect the increase in body temperature that signals ovulation has occurred. For this method to work, a woman must take her temperature every day. Temperature readings may be affected by fever, restless sleep, or varying work schedules. A couple using this method does not have sex from the end of the menstrual period until 3 days after the increase in temperature.

What is the ovulation/cervical mucus method?

The ovulation method involves changes in how much mucus is produced by the cervix and how it feels. Women who use this method learn to recognize the changes that occur around the time of ovulation. To do this, a woman checks regularly for mucus at the opening of the vagina and looks for such changes.

For most women the vagina is dry for a time just after menstruation. A sticky mucus then appears. Just before ovulation the mucus becomes wet and slippery. The last day of wetness, called the "peak" day, often occurs at the same time as ovulation. Just after the peak day, the mucus becomes thick again or may even go away, and the feeling of dryness comes back.

The safe period is the 10 or 11 days at the end of the cycle and the dry days, if any, that occur just after menstruation. The fertile period (during which the couple should not have sex) starts with the first signs of mucus and continues until 4 days after the peak day.

What is the symptothermal method?

The symptothermal method combines the temperature and ovulation methods. In addition to taking her temperature and checking for mucus changes every day, the woman checks for other signs of ovulation:

  • Abdominal pain or cramps
  • Spotting
  • Changes in the position and firmness of the cervix

This method requires that you abstain from sex from the day you first notice signs of fertility (mucus or wet feeling) until the third day after the increase in temperature or the fourth day after the peak day of mucus production.

What is the calendar method?

The calendar method also is called the rhythm method. To use this method, a woman records every day of her menstrual cycle for 6 months. She then can calculate her fertile period by looking at the calendar.

A menstrual cycle is counted from the first day of menstrual bleeding (day 1 of the menstrual cycle) to the first day of the next menstrual period. A normal menstrual cycle is about 28 days, but can range from 23 days to 35 days. The first day of the fertile phase is found by subtracting 18 days from the length of the shortest cycle. To find the last day of the fertile phase, subtract 11 days from the longest cycle. To avoid pregnancy, a couple should not have sex from the first day of the fertile phase until the last day of the fertile phase.

What is lactational amenorrhea?

Lactational amenorrhea means a woman does not have her menstrual period because of a change in hormones caused by breastfeeding. Ovulation and menstruation usually are postponed in breastfeeding women. This is because levels of a certain hormone, prolactin (which causes lactation), are increased. If a woman does not ovulate, she cannot become pregnant.

How can lactational amenorrhea be used as a method of birth control?

For this method to work, a woman must be feeding her baby nothing but milk from her breast. The time between feedings should not be longer than 4 hours during the day or 6 hours at night. The baby should always be fed on demand. The more the baby feeds and the longer the suckling per feeding, the less likely it is ovulation will return. Although feeding with formula on occasion may be fine, this may reduce the hormonal response in the woman and make ovulation more likely to return. A woman may begin ovulating before she has a menstrual period and knows that she can become pregnant again.

How long is lactational amenorrhea effective?

This method is most effective during the first 6 months of exclusive breastfeeding.


Cervicitis: Inflammation of the cervix.

Cervix: The lower, narrow end of the uterus, which protrudes into the vagina.

Fertile: Capable of reproduction.

Hormones: Substances produced by the body to control the functions of various organs.

Ovary: One of two glands, located on either side of the uterus, that contains the eggs released at ovulation and that produces hormones.

Vaginitis: Inflammation of the vagina.

If you have further questions, contact your obstetrician–gynecologist.

FAQ024: Designed as an aid to patients, this document sets forth current information and opinions related to women’s health. The information does not dictate an exclusive course of treatment or procedure to be followed and should not be construed as excluding other acceptable methods of practice. Variations, taking into account the needs of the individual patient, resources, and limitations unique to institution or type of practice, may be appropriate.

Copyright July 2014 by the American College of Obstetricians and Gynecologists. No part of this publication may be reproduced, stored in a retrieval system, posted on the Internet, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher.

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