Ka Yang, 29, from Sacramento, California, was arrested three months after the baby was found dead, as police had not until that point been able to determine the burns had come from exposure to the microwave oven. They analysed other cases where children had been harmed in a similar way, before charging Yang with the crime.
The newborn was discovered dead after a relative phoned the police. Welfare officers then took Ka Yang's other children - three boys all under seven - into care.
Yang is being held in a Sacramento County Jail. The police say they do not currently know why she allegedly put her baby into the microwave.