Teen births and pregnancies have plummeted over the past two decades, down 42 percent from 1990. Most Americans, it turns out, have no idea that we're actually in the midst of a big public health success story.

In a new survey from the National Campaign to Prevent Teen and Unplanned Pregnancy,  50 percent thought the teen pregnancy rate had gone up over that period.   Eighteen percent correctly answered that it has declined.

Young Americans were, perhaps surprisingly, the most likely to to believe the teen pregnancy rate had risen; 68 percent of those surveyed between 18 and 34 years old agreed with this.

CDC data, meanwhile, show that the teen birth rate has fallen to its lowest level since the 1940s. Researchers did see a small uptick in 2006 and 2007, but have seen rates falling steadily since then.