Police say the body was thrown away with the hospital's trash sometime between Dec. 21 and Jan. 2 and may have been hauled by train to near Ashland, Ky.
No evidence of criminal wrongdoing was found by police.
Jersey City police chief Thomas Comey says the search was called off because it was "a Herculean undertaking" with little chance of finding the tiny body.
Hospital officials say the baby was delivered stillborn on Dec. 21. The mother initially said the child was born alive.
