The baby, with its umbilical cord still attached, was found by local villagers in a rubber plantation hut near Ban None Sawan village in Tambon Khao Luang in Wang Saphung district at 2pm on Monday.
The baby was rushed to the district hospital and forwarded to Loei Hospital.
Pol Colonel Samnao Kruikrathok, chief of the Wang Saphung police station, said the force had learned that the mother is 38-year-old local resident of the village. Her house is about four kilometres from the spot where the baby was found.
Samnao said the mother disappeared after the delivery apparently because she feared her husband would harm her.
Samnao said police would try to arrest the mother and charge her with abandoning and endangering a baby.
Her sister-in-law, Yingyai (not her real name), told police that the mother already has four children, with the eldest aged 12 years and the youngest two years.
Her husband was jailed two years ago and released on Tuesday.
Yingyai said her sister-in-law’s stomach did not grow large and so her pregnancy was not noticed until last month.