The woman, a Kosovar, was placed in detention after being saved from drowning in the river along with her child on March 7th, according to a report published on Wednesday by the Neue Zürcher Zeitung.
Investigators suspected she voluntarily threw herself in the Limmat at Unterengstringen, northwest of the Zurich city centre, in a bid to kill herself and her son, although there were no witnesses, the report said.
More than five weeks after the accident, the woman remained behind bars.
Last Thursday, a hearing into the case was scheduled at the district court, but several minutes before it was set to start the woman went into labour, NZZ said.
Judges were flabbergasted by the development given that caregivers had failed to note her pregnant condition, although she had been examined at the Limmattal hospital after being pulled out of the river.
Her pregnancy also went undetected at the psychiatric clinic of the Zurich university hospital where she was subsequently treated, according to the report.
The woman was placed in an ambulance which took her to the Triemli hospital where she gave birth to a son at 9.10pm on Thursday, NZZ said.
But by Friday morning she was returned to prison, a situation that drew protests from her lawyer.
“My client was chucked out of the maternity ward at most 12 hours after giving birth to her son, it’s unacceptable,” the lawyer is quoted as saying by NZZ.
A doctor from the hospital, however, told the newspaper a woman who has given birth can be released from hospital within six hours if all goes well.
Despite the protests of her lawyer, the provisional detention of the woman has been extended until the middle of next week.
“My client is not suicidal and the prosecution has no proof,” the lawyer said.
“They should let her out and let her look after her children.”
The woman has been placed in a special cell to allow her to recover from giving birth, NZZ said.
But the mother has been separated from her newborn, who reportedly suffers from respiratory problems, although she was able to see him on Tuesday morning, the newspaper said.
UPDATE: The SDA news service reported on Thursday that the woman had been released from custody through an order from the Zurich cantonal supreme court.