A pregnant woman was trapped by a trailer on a rural property near Matamata yesterday.

The 29-year-old was trying to stop a heavy tandem car trailer from rolling down a driveway when she was knocked down and trapped by it.

She was flown by rescue helicopter to Waikato Hospital, due to the potential of a serious injury to her and her unborn baby.

Today the woman was stable, a spokeswoman for Waikato District Health Board said.