A US WOMAN has been charged with the death of a newborn baby who was found abandoned in a ditch 38 years ago, with police saying they used DNA and genealogy sites to determine she was the baby’s mother.

South Dakota resident Theresa Rose Bentaas was arrested and charged with murder and manslaughter in the 1981 death of the infant, known as Baby Andrew.

The 57-year-old told authorities last month that she’d hidden her pregnancy from her friends and family and gave birth while alone in her apartment, according to a court affidavit.

Bentaas allegedly said she then drove the baby to the area where he was later discovered, a cornfield ditch in an area called Sioux Falls.

She said she was “young and stupid” and felt sad and scared as she drove away, according to the document.

The baby died of exposure.

Bentaas, who was 19 when the baby died, later married the infant’s father and has two living adult children with him, the Argus Leader reported.

Retired Detective Mike Webb said authorities used DNA from the baby exhumed 10 years ago and DNA obtained from Bentaas through a search warrant. Webb said the father won’t be charged because he wasn’t involved.

“I couldn’t be more pleased with the results today and the arrest and the closure that we find, as well as the hard work and dedication for the pursuit of justice for Andrew,” Chief Matt Burns said.

In South Dakota, authorities submitted a DNA sample from Baby Andrew to a specialised lab, which found two possible matches using the public genealogical database GEDmatch.

Police constructed a family tree and performed a “trash pull” to collect beer and water containers and cigarette butts at Bentaas’ home.

Results from a cheek swab sample show there’s “extremely strong evidence” to support a biological relationship between Bentaas and the child, according to the affidavit.

With reporting from the Associated Press

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