This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: recent papers  obst, Subject name: Gynaecology & Obstetrics
The major contribution of the amniotic fluid after 20 weeks of gestation 
Select and explain. 
A. Fetal lung fluid, B. Fetal skin, C. Ultrafiltrate and maternal plasma, D. Fetal urine
D: Fetal urine
Answer: D: Fetal urine 
Explanation: Amniotic fluid: - * pH = 7.1 -7.3 * Specific gravity= 1.008-1.010 * Osmolality = 250 mOsm/L * Rate of amniotic fluid turnover is 500cc/hr * Completely changed and replaced in every 3 hours * Main source- fetal urine (overall) * Main source after 20 weeks- fetal urine Ref:- Mudaliar and Menon's 12th Edition; Pg num:- 28.