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. It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. 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.
In most cases, the exact cause cannot be identified. A single case may have one or more causes, including intrauterine infection, 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. In another study, all patients with polyhydramnios, that had a sonographically normal fetus, showed no chromosomal anomalies.
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 result 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.
Polyhydramnios. (2016, March 19). In Wikipedia, The Free Encyclopedia. Retrieved 17:37, March 19, 2016, from https://en.wikipedia.org/w/index.php?title=Polyhydramnios&oldid=710890694