Amniotic fluid is maximum at -- weeks of pregnancy:

Amniotic fluid measures about 50 ml at 12 weeks, 400 ml at 20 weeks and reaches its peak of 1 litre at 36-38 weeks. Thereafter the amount diminishes, till at term it measures about 600-800 ml. This fluid is faintly alkaline with low specific gravity of 1.010 An osmolarity of 250 mOsmol/litre is suggestive of fetal maturity. Note: Abnormal colour: Meconium stained green colour is suggestive of fetal distress. Golden colour in Rh incompatibility is due to excessive haemolysis of fetal RBC and production of excess bilirubin. Greenish yellow (saffron)seen in post maturity Dark coloured in concealed accidental haemorrhage is due to contamination. Dark brown amniotic fluid is found in I.U.D. The dark colour is due to frequent presence of old HbA. Ref: Textbook of Obstetrics D.C.Dutta 6th Ed Page 38.