At 4 month about how much should my baby weighing in my belly?

Quarter-pounder: At 16 wks of gestational age, the baby is still quite small--actually a bit less than 4 oz (less than a 1/4 pound). Most of the weight/size is actually amniotic fluid, placenta etc... The actual size of the guy/gal is very small--but grows more rapidly toward later in pregnancy. Maybe by 22-23 wks he/she will be a bout 1 pound. By 32-32 wks, maybe ~4lbs and by term of 40wks, 7.5 lbs. Good luck.