Abnormality of the amniotic fluid Oligohydramnios UMLS:C0079924 HP:0004638 Maternal oligohydramnios Low levels of amniotic fluid Decreased amniotic fluid index Oligohydramnios is the opposite of polyhydramnios. In normal pregnancy the amniotic fluid volume increases by about 10 ml/day until the 34th, after which it slowly diminishes. A normal amniotic fluid volume at term is about 500-2,000 ml. Oligohydramnios is defined as an AFI (amniotic fluid index) less than 5 cm or smallest vertical pocket of fluid less than 2 cm. Diminished amniotic fluid volume in pregnancy. UMLS:C3550658 SNOMEDCT_US:59566000 HP:0001562