What is the basal body temperature monitoring method?
Basal body temperature monitoring is a contraceptive method which relies on the woman monitoring her basal body temperature on a daily basis. Basal body temperature is the body’s temperature at the time of waking up, before any physical activity has been performed. The woman must also record her daily temperature measurements on a chart, so that she can easily compare changes in the temperature from day to day.
A woman’s body temperature changes throughout the menstrual cycle and changes in her body temperature coincide with hormonal changes which indicate fertile and non-fertile stages of the cycle. By monitoring her temperature every day, a woman can determine the periods of her menstrual cycle when she is and is not fertile.
In order for basal body temperature monitoring to work effectively as a contraceptive method, the woman must abstain from sex or use another contraceptive method (usually a barrier method) while she is in the fertile period of her cycle.
The basal body temperature monitoring method works by enabling women to determine the fertile and infertile periods of their menstrual cycle and avoid sex during the fertile stages.
A woman’s body temperature rises slightly after ovulation at about half way through her menstrual cycle. For example, a woman with a normal, 28 day menstrual cycle will experience ovulation about two weeks after her last menstrual bleeding and about two weeks before her next menstrual bleeding.
Ovulation takes about 24 hours and refers to the release of an egg from the ovaries. The released egg travels through the fallopian tubes to the uterus. If it comes into contact with sperm whilst in the uterus, the woman will become pregnant. If it does not meet a sperm, the egg will continue travelling through the opening of the uterus and into the vagina, where it will be expelled from the body.
Ovulation occurs in response to an increase in levels of the hormone progesterone in the woman’s body. After ovulation, progesterone levels decrease, which cause the woman’s body temperature to rise slightly. A woman can therefore identify when ovulation has passed and the fertile stage of her menstrual cycle has finished by monitoring her basal body temperature throughout the menstrual cycle. After the rise in temperature, she can be certain that she is infertile, until her menstrual bleeding begins again.
It is very important that the woman also avoid sex or use an alternative method of contraception, from the first day of the menstrual cycle (the day when menstrual bleeding commences) until a rise in basal body temperature occurs (indicating ovulation has passed). While a woman is only fertile in the 24 hours following ovulation (the time that the egg remains in her body) sperm may survive in her uterus for up to five days after sexual intercourse. So a woman can also become pregnant if she has sex without using contraception in the five days prior to ovulation. Because there is no temperature change to indicate the beginning of ovulation, it is necessary for a woman to avoid sex without contraception, from the beginning of her menstrual bleeding until her temperature drops.
It is possible for most women to use basal body temperature monitoring, most of the time. However, at times when women have a condition which causes their temperature to change (e.g. a sickness which causes fever), the basal body temperature method will be difficult to use and may be unreliable. Women with conditions affecting their body temperature must therefore use an alternative form of contraception or abstain from sexual intercourse until their body temperature stabilises.
In Australia some 4.4% of women use a type of fertility awareness method for contraception. However, there is no data showing what proportion of these women use basal body temperature monitoring, as opposed to other fertility awareness methods such as the cervical mucus monitoring or calendar method.
As with all fertility awareness based methods of contraception, it is very important to abstain from sex or use an alternative method of contraception during the fertile stages of the menstrual cycle. In order to do this, a woman requires the cooperation of her sexual partner, so it is important that partners of women using this method are also aware how the method works and why it is necessary to use other contraceptives or abstain from sex sometimes. Women may wish to take their partner to the GP or family planning clinic so that they can receive information about the basal body temperature monitoring method from a health professional.
Women using the basal body temperature monitoring method should also ensure that they obtain an alternative contraceptive method which they can use during the fertile stage of their menstrual cycle, for example condoms or a diaphragm (unless they plan to abstain from sex completely during this period). Women using the basal body temperature monitoring method should also be aware that taking emergency contraception following unprotected sex substantially reduces the risk of pregnancy. They may wish to use this method if they inadvertently have unprotected sex (e.g. by condom breaking) during the fertile period.
Women who choose to use this method must also take care to learn how to monitor and chart their basal body temperature correctly. Correct monitoring and use of the method involves:
- Measuring the basal body temperature every day, that is before getting out of bed, eating or performing any physical activity;
- Recording the basal body temperature measurement on a graph each day, so that trends in body temperature are easy to spot;
- Watching for a slight increase in temperature of 0.2-0.5oC, which indicates ovulation has passed;
- Abstaining from sex or using an alternative form of contraception from the first day of the menstrual cycle (commencement of menstrual bleeding) until three days after the 0.2-0.5oC temperature rise.
Basal body temperature monitoring is 99% effective in the first year of use, if used correctly and consistently. However, the method is less effective if the woman does not monitor her temperature accurately or if she has unprotected sex in the fertile period of the cycle (including during menstrual bleeding). Because many women have difficulty using the method correctly and consistently, about 25% of those who use fertility awareness method (including but not limited to basal body temperature monitoring) become pregnant in the first year of using the method.
For the basal body temperature monitoring method, some of the difficulty of use may be caused by external influences (e.g. rising environmental temperature) which cause the woman’s temperature to increase and for her to think that ovulation has passed when it has not. However there is also evidence that many women find the daily basal body temperature monitoring difficult and/or inconvenient.
As with other fertility based awareness methods, the benefits of basal body temperature monitoring include:
- It is a natural method and does not cause side effects;
- Women become more knowledgeable about their body changes which occur during their menstrual cycle when they use the method;
- Correctly used, it provides highly effective contraceptive protection.
The limitations of basal body temperature include:
- It is unsuitable for use while the woman has a health condition which causes her temperature to rise, for example an infectious illness;
- It requires daily monitoring of body temperature and measurements to be taken at the same time each day;
- The fertile period begins at the beginning of the menstrual cycle (as opposed to other fertility based methods in which the woman can determine if she is infertile for the first 5-7 days of the cycle). The period in which abstinence or other contraception are required is therefore longer;
|For more information on different types of contraception, male and female anatomy and related health issues, see Contraception.|
- Grimes, D. Gallo, M. Grigoreiva, V. et al. Fertility-awareness based methods for contraception: systematic review of randomised controlled trials. Contraception. 2005;72:85-90.
- World Health Organisation. Family Planning: A global handbook for providers. 2007. [cited 2009, June 20] Available from: www.who.int/entity/reproductivehealth/publications/family_planning/en/
- Richters, J. Grulich, A.E. de Visser, R.O. et al. Sex in Australia: Contraceptive Practices in a representative sample of women. Aust NZ J Pub Health. 2003;27:210-6.
- Frank, E. White, R. An updated basal body temperature method. Contraception. 1996;54:319-21.