Hello doctor my 36 days baby weight is 2.7kg his birth weight was 3 kg, do we need to go for any test to track the problem in weight gain

A. baby after birth will loss some weight and then start to gain.. this is normal.. baby should gain around 500-800g per month should be double the birth weight at 4-6months and three times the birth weight at completion of one year. exclusively breast feeding recommended for six months..