All states have legal procedures for establishing the paternity of children born 
out of  wedlock, or when the husband is found to not be the child’s father, 
pursuant to state  law:
The Commonwealth has an interest in its infant citizens having two 
parents  to provide and care for them. There is a legitimate interest in 
not furnishing  financial assistance for children who have a father 
capable of support. The  Commonwealth is concerned in having a father 
responsible for a child born  out of wedlock. This not only tends to 
reduce the welfare burden by keeping  minor children, who have a 
financially able parent, off the rolls, but it also  provides an identifiable 
father from whom potential recovery may be had of  welfare payments 
which are paid to support the child born out of wedlock.  [
Rivera v. 
Minnich, 506 A.2d 879 (Pa. 1986).]
If the mother is not married at the time of a child’s birth, a father wishing to 
establish legal paternity must legally acknowledge the child as his own. In 
some  states, this may be as simple as filing a form with the birth certificate. In 
other  states, it may require a full court proceeding similar to an adoption. If 
the mother  agrees that he is the father, a man seeking to acknowledge the 
child as his own  usually does not have to prove that he is the biologic father to 
be declared the legal  father of the child. If more than one man seeks to 
acknowledge the child or if the  mother refuses to recognize the man as the 
father of the child, the courts in most  states can order blood tests to determine 
paternity.
States also provide for the testing of potential fathers who do not voluntarily 
acknowledge their children. These lawsuits may be brought by the mother or by 
the  state on behalf of the child. It is common for the state to require an 
unmarried  woman seeking public assistance to identify the father (if known) of 
her children.  Although a state is free to establish a stricter standard of proof, 
the U.S. Supreme  Court has found that it is constitutional to establish paternity 
with a preponderance  of the evidence standard. By allowing this less strict 
standard of proof than the  standard required for termination of parental rights, 
the courts recognize the strong  societal interest in the legitimation of children. 
Once the court rules that a man is  the legal father of the child, the man has 
the same rights and duties regarding the  child as would the husband of the 
mother.