Marriage creates legal paternity for children born during its course. If a woman becomes pregnant by a man other than her husband while she's married, the law in most states presumes that her husband is the child's father even if they later divorce. However, the husband can set the record straight -- and do so as part of the divorce proceedings.
Petition to Determine Paternity
To prove that he is not the child's father, a husband can file a petition asking the court to determine the child's parentage before filing for divorce, or as part of the divorce action. If he does it before filing for divorce, the petition is a separate lawsuit. If he does it after he files for divorce, the petition or motion to determine paternity is typically incorporated into the divorce proceedings. Getting the court involved is necessary even if the husband and wife were living separately for a while. The law still presumes that the husband is the child's father as long as the divorce isn't final yet. In fact, some states take this presumption even further. For example, Washington law holds that the husband is legally the father if the child is born within 300 days of a divorce being finalized.
Forcing a Paternity Test
If a husband files a petition or motion seeking to legally establish that he is not the father of the child born during a marriage, the court – not the husband – can force the other man to take a paternity test. However, this assumes that the father's identity is known. More likely, the court will order the husband to take a paternity test. The test typically involves providing DNA samples -- and the results are highly conclusive. The test won't definitively establish that the other man is the child's father, but it will prove that the husband is not, thus removing his parental rights and responsibilities, including an obligation to pay child support.
Effect on Divorce Decree
Once the DNA test proves that a husband is not the child's father, the divorce can proceed without addressing issues of child support or custody – at least for the child in question. However, the court might require the wife to file a separate legal proceeding apart from the divorce lawsuit to establish the true father's paternity. The judge can then issue a child support order, which affects the biological father. The husband is not involved in this litigation. It would not affect the husband if the biological father takes the paternity test or if he is never identified because the court already established that the husband is not the father.
Establishing Paternity by Consent
The court may not have to order paternity testing if all three adults – the husband, wife and the child's biological father – all agree that the child is not the husband's. The husband can then remove the child from the divorce proceedings by consent in most states. This might be an option if the husband and wife were living separately for a while and she moved on to another relationship, but neither of them got around to filing for divorce. For example, in Washington, the biological father can voluntarily sign an acknowledgment that the child is his and present it to the court. He can do this in Texas as well, but the court must still rule as part of the divorce that the child is not the husband's.