This is from the book "what to expect when you're expecting"
breakdown of your weight gain
(all weights are approximate)
baby________________________ 7.5 pounds
placenta______________________ 1.5 pounds
amniotic fluid__________________ 2 pounds
uterine enlargement____________ 2 pounds
maternal breast tissue___________ 2 pounds
maternal blood volume___________ 4 pounds
fluids in maternal tissue__________ 4 pounds
maternal fat stores ______________ 7 pounds
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total average 30 pounds overall weight gain