Family Code, Art. 166

Legitimacy of a child may be impugned only on the following grounds: (1) That it was physically impossible for the husband to have sexual intercourse with his wife within the first 120 days of the 300 days which immediately preceded the birth of the child because of: (a) the physical incapacity of the husband to have sexual intercourse with his wife; (b) the fact that the husband and wife were living separately in such a way that sexual intercourse was not possible; or (c) serious illness of the husband, which absolutely prevented sexual intercourse; (2) That it is proved that for biological or other scientific reasons, the child could not have been that of the husband, except in the instance provided in the second paragraph of Article 164; or (3) That in case of children conceived through artificial insemination, the written authorization or ratification of either parent was obtained through mistake, fraud, violence, intimidation, or undue influence. (255a)