Doctors at the Max Hospital had declared the baby dead but he was found to be alive later.
Police have already registered a case of attempt to commit culpable homicide against two doctors.
Investigators have sent a notice to the hospital to join the probe and share documents pertaining to the case.
The boy was one of the prematurely born twins (boy and girl) on the morning of November 30 to Varsha at the hospital. The other baby was stillborn. The mother was brought to the hospital from a nursing home in Paschim Vihar, police had said.
The baby is undergoing treatment at a nursing home in Pitampura and doctors said he had a 40 per cent chance of survival, they added.
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