Fetal growth. There are growth curves for babies in utero. The weight estimate is just that an estimate. The weight estimate can be expressed as a percentile. Four pounds 5 ounces sounds like your baby is growing normally.
Good size baby now. At your stage of pregnancy, that is a good size. Your baby will do more rapid growth during last 6-8 wks in preparation for life on the outside world. So it is important to keep healthy diet and activities, as well as regular follow-up with your OB doc. Congrats and best of luck to you.