(Undated)  --  The March of Dimes ranks Oregon and Washington among the states with the lowest premature-birth rates in the nation.  Both states earned a grade of "A" according to the March of Dimes Premature Birth Rate Report Card.  Oregon's preterm-birth rate is seven-point-seven percent and Washington's is eight-point-one percent, compared to the national rate of nine-point-six percent.  The organization says about 380-thousand babies nationwide are born too soon each year.