Last reviewed 01/2018

Polyhydramnios is a common obstetric complication.

Polyhydramnios is a condition where there is too much amniotic fluid. The normal range is 400-1500 ml with an average of 800 ml.

On clinical examination, only volumes in excess of 2000 ml are reliably detected.

Empirically, polyhydramnios is defined as the presence of amniotic fluid pool depth of greater than 10 cm on an ultrasound scan (the normal is from 2 to 10 cm).

Aetiology of polyhydramnios is varied:

  • aneuploidy is present in 10% of fetuses with sonographic anomalies and in 1% when the ultrasound examination is considered to be normal
  • in persistent polyhydramnios, the prevalence of aneuploidy is increased (10-20%) compared with polyhydramnios with spontaneous resolution
  • other major causes of polyhydramnios include maternal diabetes, isoimmunisation disease, congenital abnormalities and multiple gestations

In a large number of pregnancies, the polyhydramnios remain unexplained despite extensive prenatal assessment (2)

Unexplained polyhydramnios has been associated with significantly higher rates of malpresentation, macrosomia, primary caesarean delivery and an increased rate of perinatal mortality (2).