An intoxicated thug lunged at his partner before grabbing her by the hair and ear as she held her baby boy.
James Brennan then pulled Charlotte Carruthers off the bed in a bedroom, which caused her to fall into a mirror at her home, a court heard.
He then repeatedly punched her face and body, giving her a burst lip and bruising during the attack.
Brennan’s violence was meted out after he attended Miss Carruthers’ Carlisle home in the early hours of April 23.
At the time Miss Carruthers was in a bedroom trying to put her nine-week-old son to sleep.
Prosecutor Andrew Scott told Carlisle Crown Court earlier today: “The complainant stated that the defendant was intoxicated and tried to lie down on the bed where he has been pushed away by the complainant.
“This has led to a verbal argument between the complainant and defendant.
“The defendant has then lunged at the complainant, grabbed her by the hair and ear, causing bruising.
“At this point she said she was holding her nine-week-old son.
“Following this, the defendant has pulled the complainant off the bed, causing her to fall into a mirror, causing injuries to her head.”
Mr Scott added: “The defendant has repeatedly punched her to the face and body, causing further injuries.”
Miss Carruthers sustained a burst lip and bruising across her upper body.
Brennan, of Upperby, Carlisle, admitted an actual bodily harm assault.
At the time he was on licence having received a lengthy jail term in early 2016 for peddling class A drugs.
David Wales, defending, said Miss Carruthers had been in “constant contact” with 25-year-old Brennan since the April assault, when the pair had been together in the bedroom.
“This was what began as a play fight and it simply got out of hand,” said Mr Wales.
However, Recorder Paul Taylor said he did not accept that submission.
Jailing Brennan for 20 months, Recorder Taylor said of the victim: “It must have been a terrifying experience for her.”
He told Brennan: “You abused your strength to assault her.”