[header] How to establish paternity in ohio [title] Show the parents were married. [step] If both genetic parents were married before the child was born, the man is considered the presumed father of the child in ohio, and there's typically no need to establish paternity. [substeps] If the child's parents are married, all the father has to do is sign the child's birth certificate. 
The parents don't have to have been married before the child was conceived. However, they do have to be married before the child is born.