<prompt> The major contribution of the amniotic fluid after 20 weeks of gestationFetal lung fluidFetal skinUltrafiltrate and maternal plasmaFetal urine  <response>: Amniotic fluid: - pH 7.1 -7.3 Specific gravity 1.008-1.010 Osmolality 250 mOsmL Rate of amniotic fluid turnover is 500cchr Completely changed and replaced in every 3 hours Main source- fetal urine overall Main source after 20 weeks- fetal urine Ref:- Mudaliar and Menons 12th Edition; Pg num:- 28. 