My baby is preterm and was born at 1.5 kgs. He is 2 months old and his weight is 3.8kgs now! So is the weight gain good or not? And how to know about their milestone’s as he is preterm born

A. good weight gain as baby generally gain around 500-800 g per month babies double the birth Weight at completing 4-6 months and three times the birth Weight at completing one year it is exclusively Breast feed recommended for six months