Single parents-babies last name?

Pennsylvania-my daughter is due June 15,2001. she is not married and not sure what last name to give the baby, hers or the fathers. are there legal issues involved? if the parents get married in the future and the baby has the mothers last name, do they have to pay to have the babies name changed?

Normaly the babies of unwed couples would take the name of mother's surname unless the unwed mother wishes to have her child to carry her child's father name.