Typically, if a child is born during a marriage then the husband is presumed to be the legal father. However, some states allow for a husband to sign an "Affidavit of Non-Paternity", and the biological father to sign an "Affidavit of Paternity". Other states provide that who ever's name is on the birth certificate makes them the "putative father" (the assumed father). All you do is to simply fill in actual father's information on the birth certificate, although this does not establish legal paternity (that can only be done via court proceedings and when you get a divorce).
To check on the law in IA, you should contact the Bureau of Vital Statistics or place a call into a family law attorney in your area.
IMPORTANT NOTICE: The Answer(s) provided above are for general information only. The attorney providing the answer was not serving as the attorney for the person submitting the question or in any attorney-client relationship with such person. Laws may vary from state to state, and sometimes change. Tiny variations in the facts, or a fact not set forth in a question, often can change a legal outcome or an attorney's conclusion. Although AttorneyPages.com has verified the attorney was admitted to practice law in at least one jurisdiction, he or she may not be authorized to practice law in the jurisdiction referred to in the question, nor is he or she necessarily experienced in the area of the law involved. Unlike the information in the Answer(s) above, upon which you should NOT rely, for personal advice you can rely upon we suggest you go to AttorneyPages.com and retain an attorney to represent you.