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Polyhydramnios (polyhydramnion, hydramnios, polyhydramnios) is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in about 1% of pregnancies.〔Alexander, ES, Spitz, HB, Clark, RA. Sonography of polyhydramnios. AJR Am J Roentgenol 1982; 138:343〕〔Hill LM; Breckle R; Thomas ML; Fries JK, Polyhydramnios: ultrasonically detected prevalence and neonatal outcome, Obstet Gynecol 1987 Jan;69(1):21-5, PMID 3540761 〕〔Hobbins JC; Grannum PA; Berkowitz RL; Silverman R; Mahoney MJ,Ultrasound in the diagnosis of congenital anomalies.,Obstet Gynecol 1979 Jun 1;134(3):331-45., PMID 453266〕 It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm.〔Y Barnhard; I Bar-Hava; MY Divon, Is polyhydramnios in an ultrasonographically normal fetus an indication for genetic evaluation?, Obstet Gynecol. 1995 Nov;173(5):1523-7.〕〔Brady K, Polzin WJ, Kopelman JN, Read JA. Risk of chromosomal abnormalities in patients with idiopathic polyhydramnios. Obstet Gynecol 1992;79:234-8.〕 There are two clinical varieties of polyhydramnios: * Chronic polyhydramnios where excess amniotic fluid accumulates gradually * Acute polyhydramnios where excess amniotic fluid collects rapidly The opposite to polyhydramnios is oligohydramnios, a deficiency in amniotic fluid. ==Causes== thumb In most cases, the exact cause cannot be identified. A single case may have one or more causes, including intrauterine infection (TORCH), rh-isoimmunisation, or chorioangioma of the placenta. In a multiple gestation pregnancy, the cause of polyhydramnios usually is twin-to-twin transfusion syndrome. Maternal causes include cardiac problems, kidney problems, and maternal diabetes mellitus, which causes fetal hyperglycemia and resulting polyuria (fetal urine is a major source of amniotic fluid). A recent study distinguishes between mild and severe polyhydramnios and showed that Apgar score of less than 7, perinatal death and structural malformations only occurred in women with severe polyhydramnios.〔Bundgaard A, Andersen BR, Rode L, Lebech M, Tabor A, Prevalence of polyhydramnios at a Danish hospital--a population-based study. Acta Obstet Gynecol Scand. 2007 ; 86(12): 1427-31.〕 In another study, all patients with polyhydramnios, that had a sonographically normal fetus, showed no chromosomal anomalies.〔 (M/C for polyhydramnio is fetal anomalies 'Williams Obstetrics, 24th Edition - Cunningham, Leveno, Bloom et al Table 11-2) but these anomalies include: *gastrointestinal abnormalities such as esophageal atresia & duodenal atresia (causing inability to swallow amniotic fluid), anencephaly, facial cleft, neck masses, tracheoesophageal fistula, and diaphragmatic hernias. An annular pancreas causing obstruction may also be the cause. *Bochdalek's hernia, in which the pleuro-peritoneal membranes (especially the left) will fail to develop & seal the pericardio- peritoneal canals. This results in the stomach protrusion up into the thoracic cavity, and the fetus is unable to swallow sufficient amounts of amniotic fluid. * fetal renal disorders that results in increased urine production during pregnancy, such as in antenatal Bartter syndrome. Molecular diagnosis is available for these conditions. *neurological abnormalities such as anencephaly, which impair the swallowing reflex *chromosomal abnormalities such as Down syndrome and Edwards syndrome (which is itself often associated with GI abnormalities) *Skeletal dysplasia, or dwarfism. There is a possibility of the chest cavity not being large enough to house all of the baby's organs causing the trachea and esophagus to be restricted, not allowing the baby to swallow the appropriate amount of amniotic fluid. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polyhydramnios」の詳細全文を読む スポンサード リンク
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