Labor pains

This refers to the cyclical, wave-like contractions of the uterus that occur repeatedly during childbirth. The wall of the uterine body that surrounds the uterine cavity is made up of muscle fibers (external longitudinal muscle and internal circular muscle) that run diagonally from left to right, and when this entire muscle contracts, it is called a labor pain, and when it is relaxed it is called intermittent. Most of the time it occurs involuntarily and is accompanied by pain, which is called labor pains.

Abnormalities in labor include weak labor, excessive labor, and convulsive labor. Labor can be strengthened or weakened by psychological effects or drug stimulation. It is used in methods such as induction of labor, which induces uterine contractions with drugs during the final stages of pregnancy, and painless childbirth.

The strength of labor pains is indicated by intrauterine pressure, which is measured using a tocodynamometer, the most commonly used being an external tocodynamometer that records uterine contractions by attaching a measuring device to the surface of the pregnant woman's body, such as the abdominal wall, but there are various other types as well. The number, strength, and duration of labor pains are measured and used as indicators of labor progress, and a tocodynamometer combined with a fetal heart rate monitor is called a labor monitoring device.

[Masao Arai]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

分娩(ぶんべん)時に周期的、波状的に反復しておこる子宮の収縮をいう。子宮腔(くう)を囲む子宮体部の壁は左右から斜方向に走る筋肉線維（外縦走筋と内輪走筋）からなり、この筋全体が収縮するのが陣痛発作であり、弛緩(しかん)している間を間欠という。多くは不随意的におこり、痛みを伴うが、この痛みを産痛という。

　陣痛の異常には微弱陣痛、過強陣痛、けいれん陣痛などがある。陣痛は精神作用や薬物的刺激などで増強させたり減弱させたりできる。妊娠末期に薬物で子宮収縮をおこして分娩を誘発する陣痛誘発法や無痛分娩などに応用される。

　陣痛の強さは子宮内圧によって表され、その計測には陣痛計が使われ、よく用いられるのは測定器を妊婦の腹壁など体表面に装置して子宮収縮を記録する陣痛外測計で、ほかにいろいろな型がある。陣痛発作の回数、強度、収縮時間などを測定して分娩進行の指標とするが、とくに陣痛計を組み合わせた陣痛胎児心拍数計は、分娩監視装置とよばれる。

［新井正夫］

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