Elsewhere in the Central Valley, 2015 ratings for Kings and Tulare County were found to have a grade of "B", with preterm birth rates of 8.9 and 9.1 percent respectively.
The nation received a "C" grade after preterm birth rates increased for the second year in a row.
In North Carolina, black women had a preterm rate of 13.5 percent, 53 percent higher than all other women in the state, the report stated.
The "March of Dimes Premature Birth Report Card" cites data from the National Center for Health Statistics (NCHS) that found the USA preterm birth rate went up from 9.6 percent of births in 2015 to 9.8 percent in 2016.
Babies born too early can face lifelong problems such as vision loss and intellectual delays.
The March of Dimes index of racial/ethnic disparity ("disparity index") in preterm birth provides a measure of the differences, or disparities, in preterm birth rates across racial/ethnic groups within a geographic area.
A baby born before 37 weeks of pregnancy is considered premature.
"The 2017 March of Dimes Report Card demonstrates that moms and babies in this country face a higher risk of preterm birth based on race and zip code", Stacey D Stewart, president, March of Dimes said. The state received a "D" grade on the annual report. "This is an unacceptable trend that requires immediate attention". Last year, African American women are 49% more likely to deliver preterm compared to Caucasian women. However, data from the March of Dimes shows preterm birth rates in East Baton Rouge and Caddo Parishes are improving along with Orleans Parish. Preterm births account for more than $26 billion annually in avoidable medical and societal costs, according to the National Academy of Medicine.
Overall, the United States earned a "C" for a premature birth rate of 9.8 percent.
The U.S. National Institute of Child Health and Human Development has more on preterm labor and birth.