Officers were called at 12.15pm on December 16 after the body of the newborn was found at an address in Norman Crescent, Rossington.
A post mortem was inconclusive and further tests are being carried out to determine the cause of death.
Two women, aged 17 and 45, were arrested on suspicion of murder.
The 17-year-old is no longer a suspect.
The 45-year-old is released under investigation.