The major contribution of the amniotic fluid after 20 weeks of gestation is :: (A) Ultrafiltrate of maternal plasma, (B) Fetal urine, (C) Fetal lung fluid, (D) Fetal skin
Answer is B. After 20 weeks as the fetal skin becomes keratinized process of diffusion is impaired. In the second half of pregnancy, the fetal kidneys become active and thereafter fetal urine becomes the main source of amniotic fluid. (refer pg no:211 Sheila 2nd edition)