Moderate prematurity refers to babies who are born between 28 and 32 completed weeks gestational age with a birth weight range between 1000 and 1500 grams (about 2 lbs 3 oz and 4 lbs). Based on their gestational age and birth weight, premature babies are placed into categories of mild, moderate and extreme prematurity. 1  Mild prematurity refers to babies who are born between 33 and 37 completed weeks gestational age and/or have a birth weight between 1500 and 2500 grams (about 3 lbs 5 oz to 5 lbs 8 oz).