Basal body temperature (BBT or BTP) is the lowest

body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...

attained during rest (usually during sleep). It is usually estimated by a temperature measurement immediately after awakening and before any physical activity has been undertaken. This will lead to a somewhat higher value than the true BBT. In women,

ovulation Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and ...

causes a sustained increase of at least in BBT. Monitoring BBTs is one way of estimating the day of ovulation. The tendency of a woman to have lower temperatures before ovulation, and higher temperatures afterwards, is known as a biphasic temperature pattern. Charting this pattern may be used as a component of

fertility awareness Fertility awareness (FA) refers to a set of practices used to determine the fertile and infertile phases of a woman's menstrual cycle. Fertility awareness methods may be used to avoid pregnancy, to achieve pregnancy, or as a way to monitor gyne ...

. The BBT of men is comparable to the BBT of women in their follicular phase.

Hormonal causes of biphasic patterns

The higher levels of

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

present during the pre-ovulatory (follicular) phase of the

menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...

lower BBTs. The higher levels of

progesterone Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

released by the

corpus luteum The corpus luteum (Latin for "yellow body"; : corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is the ...

after ovulation raise BBTs. After ovulation, the temperature will be raised by at least , for at least 72 hours, compared to the previous six days.

As a birth control method

While avoiding pregnancy

Charting of basal body temperatures is used in some methods of fertility awareness, such as the sympto-thermal method, and may be used to determine the onset of post-ovulatory infertility. When BBT alone is used to avoid a pregnancy, it is sometimes called the Temperature Rhythm method. Basal body temperature alone is most effective at preventing pregnancy if the couple abstains from intercourse from the beginning of menstruation through the third day after the basal body temperature has risen. BBTs only show when ovulation has occurred; they do not predict ovulation. Sperm typically lasts for at least three days and can survive as long as a week, making prediction of ovulation several days in advance necessary for avoiding pregnancy.

Effectiveness

There is limited evidence about the effectiveness of

family planning methods, some of which use basal body temperature as one component. About 24% of women who use any type of fertility awareness program become pregnant during the first year, compared to about 85% of sexually active women who are not trying to prevent a pregnancy. The

World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...

ranked fertility awareness methods, taken as a whole, as an "effective" method of preventing pregnancies. The WHO placed fertility awareness methods in the third tier of effectiveness, after "most effective" methods such as

IUDs An intrauterine device (IUD), also known as an intrauterine contraceptive device (IUCD or ICD) or coil, is a small, often T-shaped birth control device that is inserted into the uterus to prevent pregnancy. IUDs are a form of Long-acting rever ...

and "very effective" methods such as combined oral contraceptive pills.

Trying to conceive

Couples that are trying to conceive can use BBT to determine when the opportunity for a pregnancy during this cycle has passed.

As a diagnostic test

For infertility

Infertility due to lack of ovulation is common. BBT charts can be used to identify when and whether ovulation is taking place. Regular menstrual cycles are often taken as evidence that a woman is ovulating normally, and irregular cycles is evidence she is not. However, many women with irregular cycles do ovulate normally, and some with regular cycles are actually

anovulatory Anovulation is when the ovaries do not release an oocyte during a menstrual cycle. Therefore, ovulation does not take place. However, a woman who does not ovulate at each menstrual cycle is not necessarily going through menopause. Chronic anovul ...

or have a luteal phase defect. Records of basal

can be used to accurately determine if a woman is ovulating.

For estimating the timing of childbirth

Calculating the expected due date for a pregnancy based upon the self-reported last menstrual period is less accurate than calculating it based upon either BBT or ultrasound.

References

External links

* {{DEFAULTSORT:Basal Body Temperature Fertility awareness Gynaecology Thermoregulation