During the 40-minute attack the 22-year-old also punched the woman in the face before grabbing a kitchen knife and threatened to rape her and stab her every time she made a noise.
The woman managed to flee the property and raise the alarm. When she returned home with the police, she discovered a £500 television had been smashed and a hole had been punched through a bathroom door.
Metcalfe, of no fixed abode, was arrested and charged with making threats to kill, common assault and criminal damage, following the incident on October 31 last year.
He admitted the offences and was jailed for two years at Teesside Crown Court, and given a three-year restraining order.
Investigative Officer Heidi Weir, from Durham Constabulary, led the investigation. She said: “This was a terrifying ordeal for the woman, who not only feared for her life but for the life of her unborn child.
“She showed great bravery by escaping from the property, raising the alarm, and supporting a police investigation.
“Metcalfe is a very dangerous and controlling individual. I hope his conviction and spell behind bars will provide her with some comfort that he is off the streets and unable to harm her further.
“If you are suffering at the hands of an abuser, please come forward and speak to us.
“Taking that first step and picking up the phone may seem daunting but know that you are not alone.
“We have specially trained officers who will be with you every step of the way, who will work hard to keep you safe and help to bring your abuser to justice.
“We also work alongside several specialist agencies and charities who can offer you further help and support.
“Call us 101, or if you are in immediate danger always call 999.”