Lakshmi (24) of Vaikalipatti village in the district, drowned the baby, her third child, in the water in the tub at her house and later 'surrendered' to the Village Administrative Officer, they said.
She had been arrested and further investigation was on, police said.
They said Lakshmi was unhappy as her husband suspected her fidelity and indulged in frequent quarrels.
The woman was also dejected because the child was suffering from a congenital heart problem, which led to heavy medical expenditure, police said.
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