Basal body temperature

Japanese: 基礎体温 - きそたいおん

This refers to the temperature measured when there are no conditions that would cause temperature to fluctuate, such as eating, drinking, exercise, or emotional excitement. Usually, after 6-8 hours of restful sleep, when one wakes up early in the morning, one uses a special women's thermometer, places the mercury bulb under the back of the tongue, lightly closes the mouth, and measures the temperature for about 5 minutes before getting up. Since it measures minute differences in body temperature, a normal thermometer has 20 divisions per 1°C. A normal woman's basal body temperature shows typical changes that reflect the changes in the ovarian cycle, which occurs approximately every 4 weeks, and is therefore useful in practice for diagnosing various abnormalities in the sexual cycle, as well as for diagnosing and treating abnormalities related to pregnancy and for applications in birth control.

[Masao Arai]

Basal body temperature curve

Basal body temperature is measured every morning and entered into a set format basal body temperature chart, and then lines are drawn to create a curve (line graph). In women with normal ovarian function and ovulation, the first half of the menstrual cycle is the low temperature period and low temperature phase, and the second half is the high temperature period and high temperature phase, and a basal body temperature curve showing a low temperature phase and a high temperature phase is said to be biphasic. The temperature difference between the two should usually be 0.4°C or more. The period when the low temperature phase transitions to the high temperature phase is the ovulation period, and the last day of the low temperature phase is sometimes used as a guideline for the day of ovulation, but there is not necessarily a drop in the body temperature curve.

The relationship between the basal body temperature curve and the menstrual cycle is used as a means of knowing ovarian function, since the type of the curve in the high temperature phase reflects the luteal function of the ovaries. The type of basal body temperature curve can tell us (1) whether the ovarian function is generally good or bad, (2) what phase of the menstrual cycle it is at at the time of observation, (3) whether the curve is biphasic and ovulation precedes ovulation, or whether the curve is monophasic and anovulatory, (4) whether the menstrual cycle is regular and the period until ovulation is long or short, and (5) whether luteal phase deficiency is observed, in which the period from ovulation to menstruation is short and the temperature in the high temperature phase fluctuates irregularly, and so on, making it a useful reference for diagnosis and deciding on a treatment plan. If the high temperature phase continues for more than two weeks, it may indicate pregnancy, and if it continues for three weeks, it is almost certain to be pregnant, and is extremely useful for early diagnosis of pregnancy.

[Masao Arai]

Basal body temperature curve and birth control

Ovulation is thought to occur when the basal body temperature curve transitions from the low temperature phase to the high temperature phase. The ovulated egg is collected in the fimbria of the fallopian tube, and fertilization occurs when it meets and fuses with the sperm that have risen in the ampulla of the fallopian tube. However, the egg's fertilization ability lasts for at most 24 hours after ovulation, and sperm only survive for about three days, so if basal body temperature reaches the high temperature phase and more than three days have passed, there is no chance of fertilization. Therefore, the period from the third day of the high temperature phase until the next menstruation is a period in which fertilization does not occur, and if the menstrual cycle is regular, it can be used for contraception or to plan pregnancy. It is also one of the reasons that supports Ogino's theory that "women's ovulation period is five days, from 12 to 16 days before the next scheduled menstruation." However, when using the basal body temperature curve for pregnancy, it is important to note that the curve cannot be used to predict the day of ovulation. Ovulation is only known to have ended when the basal body temperature curve clearly indicates a high temperature, and pregnancy is not possible from three days after the temperature reaches its peak. Also, symptoms associated with ovulation such as vaginal discharge and pain during ovulation can also be used as a reference.

Menstrual cycles also vary from person to person, and even in the same person, they can be affected by various factors, and fluctuations of up to 7 days are normal, so to get to know your own menstrual cycle well, consider the basal body temperature curve for the past 6 months or so. In addition, if you write down in as much detail as possible on the temperature chart your physical condition on that day, lower abdominal pain, bloody vaginal discharge, menstrual period and amount of bleeding, and the presence or absence of blood clots, this will serve as a memo of your health and will also be useful if you have to go to the doctor for an unexpected illness.

[Masao Arai]

Basal body temperature curve and menstrual cycle
©Shogakukan ">

Basal body temperature curve and menstrual cycle

Basal body temperature curve type
©Shogakukan ">

Basal body temperature curve type

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

飲食、運動、精神感動など体温を変動させるような条件のないときに測定される体温をいう。普通、6～8時間の安静睡眠後、早朝目が覚めたら、起き上がる前に専用の婦人体温計を用い、その水銀球部を舌の裏に挟み、軽く口を閉じて約5分間測る。微少な体温の差を測るので、普通の体温計の1℃を20目盛りにしてある。正常な女性の基礎体温はおよそ4週ごとの卵巣周期の変化を反映して典型的な変化を示すので、性周期の異常に関する種々の診断をはじめ、妊娠に関する異常の診断、治療、受胎調節への応用など、実地に有用な資料となる。

［新井正夫］

基礎体温曲線

毎朝測った基礎体温を一定の様式の基礎体温表に記入し、これを線で結んだ曲線（折れ線グラフ）をいう。排卵のある正常な卵巣機能をもつ場合には、月経周期の前半は低温期間で低温相、後半は高温期間で高温相といい、低温相と高温相を示す基礎体温曲線を二相性であると表現する。両者の温度差は普通0.4℃以上あるのがよい。低温相から高温相に移行する時期が排卵期で、低温相の最終日をいちおう排卵日の目安とする場合があるが、体温曲線にかならずしも陥落が認められるとは限らない。

　基礎体温曲線と月経周期との関係は、高温相の曲線の型は卵巣の黄体機能を反映するので、卵巣機能を知る手段の一つとして利用される。基礎体温曲線の型によって、(1)卵巣の働きの全般的な良否、(2)観察時点で月経周期がどの時期にあるか、(3)曲線が二相性を示して排卵が先行している排卵性月経であるか、あるいは低温相のみの一相性の曲線で無排卵性月経であるか、(4)月経周期が規則的であるかどうか、排卵期までの期間が長いか短いか、(5)排卵から月経までの期間が短く、高温相の温度に高低の不規則な変動がある黄体機能不全症が認められるかどうか、などを知ることができるので、診断や治療方針の決定の際に参考になる。高温相が2週間以上続くときは妊娠である可能性を示し、3週間続けばほぼ妊娠とみてよく、妊娠の早期診断にきわめて有用である。

［新井正夫］

基礎体温曲線と受胎調節

排卵は、基礎体温曲線上の低温相から高温相に移行する時期におこると考えられている。排卵された卵子は卵管采(さい)で採取され卵管膨大部で上昇した精子と出会い融合したとき受精が成立するが、卵子の受精能力は排卵後長くて24時間保たれ、精子の生存期間は約3日間なので、基礎体温が高温相となって3日以上経過すれば受精の機会はなくなる。したがって、高温相の3日目を過ぎてから次回の月経までの期間は受精が成立しない期間となるわけで、月経周期が規則的な場合には避妊あるいは妊娠を計画的に行うのに利用できる。また「婦人の排卵期は次回予定月経前12～16日の5日間にある」という荻野(おぎの)学説を裏づける根拠の一つになっている。ただし、基礎体温曲線を妊娠に利用する場合、その曲線から排卵日の予測はできないことに注意する必要がある。排卵は基礎体温曲線がはっきり高温を示したときに初めて終わっていることがわかるわけで、上昇しきった日から3日以後が妊娠しない時期となる。また排卵に伴う自覚症状として帯下(たいげ)感（おりもの）や排卵期に感ずるいわゆる中間痛なども参考になる。

　月経周期はまた個人差があり、同一人でも種々の原因によっても影響を受け、7日以内の変動は正常でも認められるので、自分の月経周期をよく知るためには過去の6か月くらいの基礎体温曲線を検討する。そのほか、体温表には、その日の体調、下腹痛、血性帯下、月経期間と出血量の多少、凝血の有無などをなるべく詳しく記入しておくと、自分の健康メモになると同時に、不意の病気で診察を受ける場合にも役だつ。

［新井正夫］

[参照項目] | 荻野学説 | 月経 | 受胎調節 | 性周期 | 妊娠 | 避妊法

基礎体温曲線と月経周期

基礎体温曲線の型

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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