Polyhydramnios refers to an excess of amniotic fluid, i.e., more than expected for the gestational age, which causes uterine distention. The etiology is unknown in approximately 70% of cases, but it may be caused by maternal conditions (e.g., diabetes, rhesus incompatibility) or fetal abnormalities (e.g., chromosomal or structural). Diagnostics include physical examination, ultrasound, and blood tests. Management involves , amnioreduction if there are severe symptoms , and treatment of the underlying cause. Complications include fetal malposition, umbilical cord prolapse, premature birth, and premature uterine contractions.
- Typically idiopathic (∼ 70% of cases) 
- Gastrointestinal (e.g., : , )reduced swallowing and absorption of amniotic fluid
- CNS: ; (leads to impaired swallowing of amniotic fluid, leakage of cerebrospinal fluid, and increased urination due to lack of fetal ADH), (due to leakage of cerebrospinal fluid) 
- Pulmonary: cystic lung malformations
- Multiple pregnancy: twin-to-twin transfusion syndrome
- Fetal anemia 
- Intrauterine infections (e.g., )
- Maternal conditions
- All patients should obtain a regular biophysical profile with a nonstress test.
- Amnioreduction: drainage of excess amniotic fluid
- Treatment of underlying cause (e.g., glycemic control in diabetic mothers, intrauterine exchange transfusion in hemolytic disease of the newborn)