At a routine third-trimester scan, the deepest vertical pocket of amniotic fluid measures 11 cm. This finding defines:

• A Normal amniotic fluid volume
• B Oligohydramnios
• C An uninterpretable measurement requiring repeat after 48 hours
• D Polyhydramnios ✓

Explanation

Amniotic fluid is quantified either as the amniotic fluid index or the single deepest vertical pocket. Polyhydramnios is defined as a single deepest pocket greater than 8 cm (or AFI above the 95th centile, roughly above 24 to 25 cm), and oligohydramnios as a deepest pocket under 2 cm. A pocket of 11 cm therefore meets the definition of polyhydramnios, and the commonest cause overall remains idiopathic, with maternal diabetes and fetal anomalies being important associations.

Reference: Callen's Ultrasonography in Obstetrics and Gynecology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.