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High or Low Amniotic Fluid Levels
OligohydramniosPolyhydramniosPregnancy

Amniotic fluid volume is one of the key measurements on growth and monitoring scans. Too little or too much can indicate problems with the baby or placenta — though both conditions have a wide range of causes and outcomes.

How Fluid Is Measured

MethodWhat It MeasuresNormal Range
Amniotic Fluid Index (AFI)Total depth in four quadrants5–25 cm
Single Deepest Pocket (SDP)Deepest single pocket2–8 cm

Oligohydramnios: Too Little Fluid

Oligohydramnios is diagnosed when the AFI falls below 5 cm or SDP below 2 cm. In the second half of pregnancy, amniotic fluid is mostly fetal urine — so low fluid often means the baby is not urinating enough. This can result from:

  • Kidney problems or absent kidneys (renal agenesis)
  • Placental insufficiency reducing blood flow to the baby
  • Rupture of membranes (leaking fluid)
  • Post-term pregnancy (fluid naturally decreases after 40 weeks)
  • Certain blood pressure medications (ACE inhibitors)

Polyhydramnios: Too Much Fluid

Polyhydramnios is diagnosed when AFI exceeds 25 cm or SDP exceeds 8 cm. Since the baby swallows amniotic fluid, too much fluid can mean the baby is not swallowing effectively:

  • Gastrointestinal atresia (blockage preventing swallowing)
  • Fetal anaemia or heart failure
  • Maternal gestational diabetes causing excess fetal urination
  • Twin-to-twin transfusion syndrome in identical twin pregnancies
  • Idiopathic (no cause found) — accounts for about 50–60% of cases

How Each Condition Is Managed

ConditionManagement Approach
Mild oligohydramniosIncreased hydration, serial scans, Doppler monitoring
Severe oligohydramniosPossible early delivery depending on cause and gestation
Mild polyhydramniosRegular monitoring, rule out GDM
Severe polyhydramniosTherapeutic amniocentesis to drain excess fluid; risk of preterm labour

Warning

Sudden loss of amniotic fluid — even a slow trickle — requires immediate medical assessment. Do not wait.