<prompt> Birth weight doubles by?3 months5 months9 months12 months  <response>: Ans. b 5 monthsRef O.P Ghai 8th ed4Birth weight doubles at 5 months, triples in an year and is four times at 2 years and becomes 5 times at 3 years.Note: Newborns lose 10 of body weight in first ten days due to loss of extracellular water, after which they gain 25-30gms per day for first 3 months of life. 