A lower than normal quantity of amniotic fluid in the amniotic sac as compared to normal values. Typically associated with an amniotic fluid index (AFI) of less than 5 cm or a single maximum vertical pocket (MVP) of less than 2 cm. The disease is oligohydramnios (MONDO_0005881, a Monarch Disease Ontology term). Also known as: antepartum oligohydramnios, delivered oligohydramnios, oligohydramnios (disease), oligohydramnios - delivered.