Oligohydramnios is almost always associated with an inability to excrete urine and is most commonly associated with bilateral renal agenesis, posterior urethral valves (in males), and sometimes placental insufficiency. Any profound oligohydramnios can cause Potter sequence. In this question, urethral obstruction as an answer option is wrong because it causes oligohydramnios (the question was asking about polyhydramnios) because it leads to decreased fetal urine output and decreased amniotic fluid production by the fetus.
submitted by โshak360(19)
Polyhydramnios is almost always associated with an issue with the baby's ability to swallow amniotic fluid, preventing its recycling and resulting in the overproduction of amniotic fluid. Inability to swallow may be due to esophageal or duodenal atresia or anencephaly. It can also be associated with maternal diabetes, fetal anemia, and multiple gestations.