Oligohydramnios occurs when the volume of amniotic fluid that surrounds the baby is less than normal. Amniotic fluid levels change daily, so repeat ultrasounds are recommended. The incidence rate of oligohydramnios ranges from .5% to 8% of all pregnancies.
A detailed ultrasound of the fetal anatomy is recommended because, while oligohydramnios can be an isolated condition, it is often associated with aneuploidy, chromosomal abnormalities, intrauterine growth restriction, malformations of the brain, heart, and skeleton, and renal anomalies. Renal anomalies account for 11% of all cases of oligohydramnios.
When oligohydramnios is present prior to 22 weeks gestation, there is a higher likelihood of pulmonary hypoplasia and other congenital malformations, resulting in a poorer prognosis. Significant oligohydramnios in the second trimester is associated with a high perinatal mortality rate of 60%. Oligohydramnios in conjunction with intrauterine growth restriction has a perinatal mortality rate ranging from 10-19%. The recurrence risk depends on the underlying cause and associated diagnoses.