What defines oligohydramnios in terms of amniotic fluid volume?

Oligohydramnios is defined as a condition characterized by a decreased volume of amniotic fluid surrounding the fetus. According to standard medical definitions, oligohydramnios is diagnosed when the amniotic fluid volume is less than 500 mL. Amniotic fluid plays critical roles in fetal development, including cushioning the fetus, allowing for normal growth, and facilitating certain physiological developments. When the volume is below this threshold, it can lead to complications, such as fetal distress and developmental issues.

The other options represent volumes of amniotic fluid that would not classify as oligohydramnios. For instance, volumes over 2,000 mL would indicate polyhydramnios, which is an excessive amount of fluid. A volume of exactly 1,000 mL falls within a normal range, while a volume between 500 and 1,000 mL may lean towards normal or borderline conditions but would require clinical correlation and further assessment. Thus, identifying oligohydramnios hinges on that crucial cut-off of less than 500 mL.