If I am pregnant by a man other than my husband can the biological father sign the birth certificate???

Under Wisconsin law, putting a person's name on a birth certificate has no legal effect. The only way to establish paternity is by either both parties signing a voluntary acknowledgment of paternity or by one of the parties filing a formal paternity case in court. Further, since you are married, there is a presumption that your husband is the father of the child. If you file for divorce, the judge will not let you get divorced until it can be determined whether your husband is or is not the biological father. This usually means the baby has to be born if a woman is currently pregnant, and requires DNA testing. I recently wrote a blog at our web site under family law issues on this  very topic.