Tennessee’s grade on premature births is lower than last year’s on a nationwide scale — but so is the state’s premature birthrate.

The March of Dimes, in its annual Premature Birth Report Card, gave Tennessee a D, based on the 2013 statewide preterm birthrate of 10.8 percent.

But the preterm birthrate has actually improved since the state’s 2014 C-grade report card, from 12.6 percent. On the 2013 report card, also a C, the statewide preterm birthrate was 12.5 percent.

What’s changed is the March of Dimes’ methodology. With its new grade ranges, Tennessee would have flunked in 2014 and 2013, since any rate greater than 11.5 percent is an F. To receive an A, a state’s preterm birthrate would have to be 8.1 percent or less. Knox County, at 8.4 percent, would almost qualify.

Read more from our news partners at the Knoxville News Sentinel.