[The First Aria]

It and of itself does not add breast tissue, But due to the ducts filling it does cause the breast to swell.  But the majority of women, once they stop lactating, they shrink w/out adding more fat or breast tissue.  That why a lot of women have saggy breasts after pregnancy and stopping breast feeding.  Its like blowing a balloon up to almost bursting size, then after a few days letting half the air out of it.