(a) If a parent-child relationship does not exist between the child and any man, a certificate from the vital statistics unit signed by the registrar that a diligent search has been made of the paternity registry maintained by the unit and that a registration has not been found pertaining to the father of the child in question must be filed with the court before a trial on the merits in the suit for termination may be held.
(b) In a proceeding to terminate parental rights in which the alleged or probable father has not been personally served with citation or signed an affidavit of relinquishment or an affidavit of waiver of interest, the court may not terminate the parental rights of the alleged or probable father, whether known or unknown, unless a certificate from the vital statistics unit signed by the registrar states that a diligent search has been made of the paternity registry maintained by the unit and that a filing or registration has not been found pertaining to the father of the child in question.