The woman, who was in the eighth month of her pregnancy, died in the early hours of Saturday morning, Il Messaggero reported.
On Friday evening she went to San Pio X, a clinic close to her home where medics had been keeping track of her pregnancy, complaining of lower back and abdominal pain.
But after carrying out checks, the woman, who had a four-year-old child, was given the all-clear and told to return should the pain recur.
In the early hours of Saturday morning she was found unconscious by her husband, who called an ambulance. By the time paramedics arrived, the woman had fallen into cardiac arrest and later died at Milan's Niguarda hospital.
Doctors tried to save her unborn baby by performing an emergency caesarean section, but were unsuccessful.
Roberto Maroni, the president of the Lombardy region, called for “immediate checks” to be made.