NSW man held after pregnant woman attacked

A man has spent the night behind bars after a pregnant Sydney woman was allegedly punched and threatened with a knife before her car was stolen.

The 24-year-old woman was home alone in Sydney's west when she was allegedly struck and threatened by a knife-wielding man, while two others tried to get into her house around 1.30am on Friday.

One man has been charged over the violent attack and will face court on Saturday.

The mother-of-three has told the Seven Network she was grabbed as she stood in the front yard of her Seven Hills home.

The trio fled the scene in the woman's Commodore sedan, which was later found burnt out in nearby Toongabbie, police say.

A man was arrested at about 11am on Friday and charged with aggravated assault, breaking and entering, damaging property and stealing.

He was refused bail and will appear at Parramatta Local Court on Saturday.

The woman was checked by paramedics but was uninjured.