When she returned Paku pushed her back into the bedroom, on to the bed and punched her again. He then leant towards her and bit her on the bottom lip.
The woman suffered redness and tenderness to her head and a cut to her lip.
Defence lawyer Louise Elder said Paku accepted the assault took place but denied biting her on the lip.
Ms Elder said Paku will be attending a stopping family violence programme this month.
She said a protection order was in place but "there is a baby due any day".
Judge Tony Walsh said Paku had a previous conviction and had appeared in March 2011 on a charge of assault.
Judge Walsh said the assault was of particular concern as the woman was pregnant.
"You are about to become a father, this type of violence is totally unacceptable ... if she had suffered a really serious injury, or you had killed her, you would have had to live with that for the rest of your life."
He sentenced Paku to nine months' supervision and 60 hours' community work.