La. Civ. Code art. 190.1
If blood or tissue sampling indicates by a ninety-nine and nine-tenths percentage point threshold probability that the biological father is the father of the child and he is not the husband or former husband presumed to be the father of the child, then the husband or former husband presumed to be the father of the child, the mother, and the biological father of the child may execute a three-party acknowledgment in authentic form declaring that the husband or former husband is not the father of the child and that the biological father is the father of the child. When a three-party acknowledgment is executed, the husband or former husband is not presumed to be the father of the child. The biological father who has acknowledged the child by three-party acknowledgment is presumed to be the father of the child.
To have effect, this acknowledgment shall be executed no later than ten years from the day of the birth of the child but never more than one year from the day of the death of the child. These time periods are peremptive.
La. C.C. § 190.1