Polyhydramnios is a classical sonographic sign of obstruction, but is not always present, Heydanus et al report this sign in 71% of small bowel obstructions.

• 肠管梗阻一般会出现羊水过多，但不总是会出现。Heydanus等人报导说有71%25的小肠梗阻会出现这种表现。