Polyhydramnios refers to a situation where the amniotic fluid volume is more than expected for gestational age.

It is generally defined as:

It can occur in approximately 1-1.5% of pregnancies.

The patient may clinically present as a large for dates uterus

Polyhydramnios occurs as a result of either increased production or decreased removal of amniotic fluid. The aetiology of polyhydramnios can be due to a vast variety of maternal and fetal disorders. 

It is usually detected after 20 weeks (often 3rd trimester).

The potential causes of polyhydramnios are variable including:

Polyhydramnios is associated with the poor outcome if present in combination with intrauterine growth restriction (IUGR); usually seen in aneuploidies 18,13, and 21.

This classification is general consensus based on common practices at the time of writing (July 2016) but this varies according to countries and gynaecologist association guidelines.

Some classify the severity of polyhydramnios as 

  • mild: single deepest pocket at 8-11 cm or AFI 25-30
  • moderate: single deepest pocket at 12-15 cm or AFI 30.1-35
  • severe: single deepest pocket >16 cm or AFI >35

The risk of the following obstetric complications is increased when polyhydramnios is present due to over-expansion of the uterus13:

  • maternal dyspnoea
  • premature membrane rupture
  • preterm labour
  • abnormal fetal presentation
  • umbilical cord prolapse
  • postpartum haemorrhage: due to reduced uterine myometrial tone



The prognosis is variable dependent on associated conditions. Usually minimal or no interventional required for idiopathic mild uncomplicated cases. Options include:

Ultrasound - obstetric
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Article information

rID: 4797
Section: Gamuts
Synonyms or Alternate Spellings:
  • Hydramnios

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