Oligohydramnios, or low amniotic fluid, is when a pregnant woman has too little amniotic fluid. Amniotic fluid is the fluid that surrounds the baby in the uterus. It is important for the development of the fetus. Because oligohydramnios has many causes, drinking plenty of water may not resolve the low amniotic fluid condition if other causes of oligohydramnios are not identified and corrected.