The clear fluid contained within the AMNION that surrounds the FETUS in the womb and protects it from external pressure. The fluid, comprising mainly water, is produced by the amnion and is regularly circulated, being swallowed by the fetus and excreted through the kidneys back into the amniotic sac. By the 35th week of pregnancy there is about 1 litre of fluid, but this falls to 0.5 litres at term. The amniotic sac normally ruptures in early labour, releasing the fluid or ‘waters’.