 Subjects and Methods: Women with normal AF index and gestational age between the 33 and 36 weeks without maternal complications were randomized into three groups isotonic solution, water, control. The isotonic solution and water groups were instructed to drink 1.5L of respective solution; the control group was instructed to drink 200mL of water. AF index was measured before and after hydration. The investigator performing the AF index was blinded to the subjects group. 