True regarding maternal plasma osmolality during pregnancy: (A) Maternal plasma osmolality decreases early in pregnancy, (B) Maternal plasma osmolality increases throughout pregnancy, (C) Maternal plasma osmolality does not change during pregnancy, (D) Maternal plasma osmolality is affected most by increases in sodium
Answer is A. Increased water retention in pregnancy is normal physiological change of pregnancy. It is mediated by fall in plasma osmolality induced by resetting osmotic thresholds for thirst and vasopressin secretion.