<prompt> The major contribution of the ammiotic fluid after 20 weeks of gestationsUltrafiltrate and maternal plasmaFoetal urineFoetal lung fluidFoetal skin  <response>: Foetal urine: Ref: 37, 214, 218, 464-D Obstetrics - G. Chamberlain 7thAMNIOTIC FLUIDProduced: In early pregnancy, from amnion over placenta and sacLate pregnancy: from fetal urine as wellVolume: Increase to 38 weeks 500 - 1500 ml50 ml: 12 weeks500 ml: 24 weeks1000 ml: 36 weeksOsmolality: Decreases in late pregnancyCreatinine: Increases in late pregnancyAcid - base: Normally accumulation of CO2 and fixed acid causes a slight reduction in pH About 7.15 - 7.20 The foetus drinks about 400 ml of liquer every day at term and equal amount is excreted in the urine The water in the amniotic fluid is completely changed and replaced in every 3 hours. Abnormal colour- Meconium stained green - Foetal distress Breech or transverse- Golden colour - Rh. Incompatibility- Greenish yellow Saffron - Post maturity- Dark coloured - concealed accidental hemorrhage- Dark brown tobacco juice - IUD Amniotic Fluid Index AFI - An AFI between 5 and 25 cm is normal and an AFI less than 5 cm 10 centile indicates oligohydramnios and AFI more than 25 cm 95 centile for gestational age indicates Polyhydramnios 464-D 