Amniotic fluid

Generally speaking, it is the physiological fluid that fills the amniotic cavity, also called amniotic fluid, and is secreted by amniotic epithelial cells. In other words, it is the fluid that fills the uterine cavity surrounded by the amniotic membrane during pregnancy, and has the role of protecting the fetus, and is also called amniotic fluid. It also helps dilate the cervix during childbirth. Amniotic fluid is colorless in the early stages of pregnancy, but becomes cloudy white in the late stages as it contains the fetus's skin, vernix caseosa, and downy hair. The normal amount of amniotic fluid at the end of pregnancy is generally 600 to 800 milliliters, but there are abnormalities in the amount of amniotic fluid, such as too much or too little. Of these, oligohydramnios is rare and difficult to diagnose definitively during pregnancy, and it can cause fetal movement to feel like severe pain, and the fetus's development is hindered due to its difficulty in moving, leading to various morphological abnormalities such as funnel chest, in which the rib cage is depressed.

Polyhydramnios is a condition in which excess amniotic fluid causes damage to the mother and child, and is generally around 2 liters. There are chronic cases where the amount gradually increases over several months, and acute cases where the amount increases rapidly within a few days, and the abdominal circumference can reach more than 1 meter. The cause is a quantitative abnormality that appears if there is a disorder in the pathways of production, circulation, and regression of amniotic fluid. In other words, it is based on excessive secretion or insufficient absorption due to circulatory disorders in the mother and/or fetus, and is diagnosed based on the fact that the abdomen is large compared to the number of months of pregnancy, the vibration is significant, and the fetus is highly mobile. It becomes difficult to determine the position of the fetus and to hear the heartbeat. The pregnant woman also feels pressured and has difficulty breathing. In addition to complications such as twins, diseases of the mother's heart and kidneys, and morphological abnormalities of the fetus, various abnormalities such as weak labor and premature rupture of membranes, and premature birth are likely to occur. Treatment is considered extremely difficult, and in acute cases, induced abortion is performed, and in chronic cases, bed rest is maintained and natural childbirth is attempted as much as possible.

[Masao Arai]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

一般には羊膜腔(くう)を満たす生理的液体のことで、羊膜液ともよばれ、羊膜上皮細胞から分泌される。すなわち、妊娠時に羊膜に包まれた子宮腔を満たす液で、胎児を保護する役目をもち、胎水ともよばれる。また、分娩(ぶんべん)時には子宮口の開大にも役だつ。羊水は、妊娠初期には無色であるが、末期になると胎児の皮膚、胎脂、うぶ毛なども含まれて白濁する。妊娠末期の羊水量は一般的に600～800ミリリットルを普通量としているが、羊水量の異常には過多と過少がある。このうち、羊水過少症はまれであり、妊娠中に確定診断することがむずかしく、胎動を激痛のように感じたり、胎児にとっては動きにくくて発育が妨げられ、胸郭がへこむ漏斗(ろうと)胸など各種の形態異常を招きやすい。

　羊水過多症は、過剰な羊水量によって母児への障害をもたらすもので、一般には2リットル前後のことが多い。数か月かかって徐々に増量する慢性のものと、数日のうちに急速に増える急性のものがあり、腹囲が1メートル以上にも達する。原因は、羊水の産生、循環、後退の経路に障害があれば量的異常が現れるわけで、要するに母体と胎児、あるいはその両者の循環障害による分泌過剰または吸収不全に基づくものであり、妊娠月数に比して腹部が大きく、その波動が著明で、胎児の可動性が大であることなどから診断される。胎児の位置がわかりにくく、心音も聞き取りにくくなる。妊婦も圧迫されて呼吸が苦しくなる。双胎、母体の心臓や腎(じん)臓の疾患、胎児の形態異常などを合併するほか、微弱陣痛や早期破水など種々の異常や早産がおこりやすい。治療はきわめて困難とされ、急性の場合は、人工妊娠中絶を行い、慢性の場合には就床安静を守り、なるべく自然分娩を行わせる。

［新井正夫］

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