Police said the woman, who works as ayah in households and local health facilities on contract, was arrested at Sarbamangalapara locality in Burdwan town and the newborn recovered from her possession.
On being questioned the ayah gave incoherent replies following which she was arrested, a police officer said but did not disclose her name.
To a question, the officer said apparently the incident looked unrelated with the sensational child trafficking racket in Kolkata and two neighbouring districts.
Prima facie the woman's claim about the baby being her sister's daughter appeared true, police said.
A raid also took place in two nursing homes of Burdwan town, the officer said but again refused to name the nursing homes.
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