My baby boy was born prematurely at 33 weeks(7 months). What age shall I take take to follow weight chart ? ie. from Actual delivery date at 33 weeks(7 months) or from his estimated date of delivery ta end of 40 weeks(9 months)? He is currently 3.6 kgs after 3 months from Actual Date of delivery, which is very underweight. If we take age as 1 month from Estimated Date of delivery(9 months), his weight is good.