Water breaks - Hasui

Also known as amniotic sac rupture, this occurs when the amniotic sac, which helps open the birth canal during childbirth, becomes extremely tense and eventually ruptures due to the internal pressure, spilling out 20 to 30 milliliters of pre-amniotic fluid. It is normal for this to occur after the external cervical os has fully dilated, and premature rupture of membranes before labor begins or before the external cervical os has fully dilated is considered abnormal. The rupture of the amniotic sac is not always observed near the presenting part of the fetus, and it can sometimes occur above the cervical os, which is called high rupture of membranes. In such cases, as the fetal head enters the pelvic cavity as labor progresses, the ruptured area is compressed and blocked, a new amniotic sac is formed, and membranes rupture occurs again. This is called double rupture of membranes.

Abnormal rupture of membranes is common among older first-time mothers, and can occur due to cervical rupture, narrow pelvis, abnormal fetal position, hypertonic labor, cervical inflammation, sudden abdominal pressure, and excessive dilation of the uterine wall.

[Masao Arai]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

胎胞(たいほう)破裂ともいい、出産時に産道を開大するのに役だつ胎胞が極度に緊張し、ついには内圧に耐えられずに破裂し、胎胞内にあった20～30ミリリットルの前羊水を流出することをさす。外子宮口の全開大後におこるのが正常であり、陣痛のくる前の前期破水や外子宮口全開大前におこる早期破水などは異常とされる。また、胎胞の破れる部位は胎児先進部付近だけに認められるとは限らず、ときには子宮口よりも上部でおこることもあり、高位破水とよばれる。このような場合、分娩(ぶんべん)進行によって児頭が骨盤腔(くう)内に進入すると、破れた部分が圧迫閉塞(へいそく)されて新たに胎胞が形成され、再度破水がみられる。これを重複破水という。

　破水の異常は高年初産婦に多く、子宮頸管(けいかん)破裂、狭骨盤、胎児位置異常、過強陣痛のほか、頸管の炎症、急激な腹圧、子宮壁の過度拡張などの場合におこる。

［新井正夫］

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