There are many changes that occur in a woman’s body during pregnancy that contribute to the healthy weight gain experienced. Here is a list of approximate values of what tissues increase in volume or size to impact change in weight: 

• Amniotic fluid: 2-4 lbs 
• Adipose tissue: 4-7 lbs 
• Blood components: 2-4 lbs 
• Breast: 2-4 lbs (up to 8 lbs when milk comes in) 
• Fluid (Extracellular): 3-10 lbs 
• Fetus: 5.5-7.5 lbs 
• Placenta: 1.5-4 lbs 
• Uterus: 2 lbs

Click here for more on healthy amount of weight to gain during pregnancy and other pregnancy health matters.