Excess amniotic fluid surrounding an unborn baby in the womb. The condition should be suspected if the uterus is larger than the stage of pregnancy would suggest. At the same time the excess fluid makes the child very mobile, and this can be felt clearly through the abdominal wall. The condition is caused by abnormalities in the foetus which prevent it from drinking the fluid, such as lack of a swallowing reflex or a closed oesophagus. The condition also sometimes accompanies diabetes mellitus and rhesus incompatibility.