Neil Andrew Thomas Reid, of Chorley Road, Walton-le-Dale, Preston, has admitted criminal damage after the incident at their home on Further Field in Bamber Bridge on September 3.
When the charge was put to him the 36-year-old said: “Yeah, I’m sorry I’m guilty.”
Preston Magistrates’ Court was told the victim was 11 weeks pregnant with their child when he started arguing with her in the middle of the night and accused her of “cheating”.
In a statement she said the incident had caused her “great stress”.
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Prosecuting, Beth Pilling said: “The complainant is the partner of the defendant. She was 11 weeks pregnant at the time.
“She says at 2.25 am she was in the address, the defendant was with her.
“They started to argue and he accused her of cheating.
“She told him it wasn’t true and he needed to go as kids were asleep upstairs.
“He did leave reluctantly but returned and at 2.35am he was looking through the kitchen window and started to kick at front door and she heard a thud at the front window.
“She was preoccupied settling her children back to sleep and did not realise it had been smashed.”
In an interview Reid accepted he smashed the window.
The court heard he was remorseful and said he had come back to the house because he wanted to get his things, but the woman had locked the doors.
The bench was told he had seven convictions including shoplifting and aggravated vehicle taking.
Representing himself he said the couple has since reconciled, adding: “I didn’t mean to do it, she’s pregnant with my child.
“I miss my kids and I’m just sorry for doing it.
“It was due to my mental health - I wasn’t taking my meds at the time but I realise that I need my medication.”
Reid was ordered to pay Â£150 compensation to the woman but no order for costs was made.