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 temperatur ...

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

follicular phase The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle (or, in primates for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a fully ...

Hormonal causes of biphasic patterns

The higher levels of

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

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 make pregnancy possible. The ovarian cycle controls the production and release of eggs ...

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 majo ...

released by the

corpus luteum The corpus luteum (Latin for "yellow body"; plural 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 t ...

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. The rise in temperatures can most commonly be seen the day after ovulation, but this varies and BBTs can only be used to estimate ovulation within a three-day range. If pregnancy does not occur, the disintegration of the corpus luteum causes a drop in BBTs that roughly coincides with the onset of the next menstruation. If pregnancy does occur, the corpus luteum continues to function (and maintain high BBTs) for the first trimester of the pregnancy. After the first trimester, the woman's body temperature drops to her pre-ovulatory normal as the placenta takes over functions previously performed by the corpus luteum. Very rarely, the corpus luteum may form a

cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

. A corpus luteum cyst will cause BBTs to stay elevated and prevent

menstruation Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of ...

from occurring until it resolves, which could take weeks or months.

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 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 gyneco ...

, 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 fertility awareness 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 specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...

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 and "very effective" methods such as

combined oral contraceptive pills The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. The pill contains two important hormones: progesti ...

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 anovulat ...

or have a

luteal phase defect The corpus luteum (Latin for "yellow body"; plural 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 th ...

. Records of basal

can be used to accurately determine if a woman is ovulating, and if the length of the post-ovulatory (luteal) phase of her menstrual cycle is long enough to sustain a pregnancy.

For pregnancy

Most pregnancy tests are not accurate until two weeks after ovulation. Knowing an estimated date of ovulation can prevent a woman from getting false negative results due to testing too early. Also, 18 consecutive days of elevated temperatures means a woman is almost certainly pregnant.

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