If a girl younger than 16 gives birth in Mississippi and won't name the father, a new state law says authorities must collect umbilical cord blood and run DNA tests to prove paternity.
Experts say the law is likely the first of its kind nationwide.
Supporters say the law is intended to chip away at Mississippi's high teen pregnancy rate.
Gov. Phil Bryant says it could lead to prosecution of men who have sex with underage girls.
Critics say that though the procedure is painless, it invades the medical privacy of the mother, father and baby.
The law took effect July 1 but hasn't been used yet.
The state medical examiner is setting administrative rules for how cord blood samples will be collected and stored.