Police later arrested a 25-year-old man after the incident, which took place yesterday afternoon outside the Sunderland Royal Hospital where the women had been to an ante natal clinic.
Doctors performed an emergency operation on Amanda Hunter, 20, who was 38 weeks in to her pregnancy.
She had been stabbed in the stomach, chest, back and shoulder. Doctors said the knife had cut into her womb and nicked the unborn baby but both mother and child were said to be stable after the surgery.
Shocked onlookers initially thought the man was punching the distraught woman but when security guards arrived they realised that he was holding a knife.
Security officers John Atkinson and Colin Boyd chased him for 100 yards through the hospital grounds before overpowering him.
Mr Atkinson said: "He waved the knife at us as we chased him but thankfully we got a chance to overpower him and detained him until police arrived." The woman, who is not being named, was rushed into the hospital where staff induced the birth of her baby, a 7lb boy.
The hospital's Accident and Emergency consultant David Parkins said: "She was conscious during treatment and talked to us throughout. She suffered a collapsed lung and we had to insert a chest drain.
"The baby was delivered by Caesarean operation. The mother is now on a surgical ward and the child is in the special care baby unit."
Hospital spokesman Graham Howard said: "She was very fortunate to be so close to accident and emergency and all of the equipment and expertise needed to treat her."
Detective Chief Inspector Dave Jackson, of Sunderland City CID, said: "This was a terrible incident but I would like to assure people attending the hospital that there is no risk to anyone else.
"I would also like to commend the actions of hospital staff who showed great courage in detaining the assailant at great risk to themselves."
Police were last night questioning a 25-year-old man about the incident.Reuse content