Less than one in ten babies was born preterm in the U.S. in 2014, but the rate is nearly twice that high in some cities. A new report card released by the March of Dimes grades the 100 largest U.S. cities based on how many mothers living there give birth before 37 weeks of pregnancy, which can lead to serious health complications for babies.

The preterm birth rate in 2013, the latest year with local data, ranges from 7.2 percent in Portland, Ore., to 18.8 percent in Shreveport, La. (See full list below.)

Dr. Siobhan Dolan, an obstetrician at Montefiore Medical Center in New York and a March of Dimes medical adviser, said the cause of preterm births isn’t the same everywhere, so focusing on local rates can help doctors, parents and researchers prevent them. “For example, smoking has a bad effect on health for everyone and pregnant women in particular," Dolan said. "There’s parts of the country where 20 percent of pregnant women still smoke."

Still, she said that "there’s not one simple answer, there’s not one pill or one shot that will make the difference,” Dolan said.

The national preterm birth rate spiked in the mid-2000s. Dolan said a number of initiatives have contributed to the decline, including new guidelines that recommend doctors only implant one embryo in at a time during an in-vitro fertilization cycle; doctors discouraging early elective delivery; better access to pre-natal care thanks to the Affordable Care Act; and making sure women have access to birth control to space births the ideal 18 months apart.

Dolan added, “in about half of cases of preterm birth, there’s no identified ‘cause’, quote unquote. We need more research to provide insight into why some women deliver preterm.” She said researchers are not sure why women of some races are more likely to deliver preterm babies."

List of cities by premature birth rate in 2013

City State Rate Grade
Portland OR 7.2 A
Oxnard CA 7.8 A
St. Paul MN 8 A
Seattle WA 8.1 A
Oakland CA 8.2 B
Santa Ana CA 8.2 B
Lincoln NE 8.2 B
Modesto CA 8.3 B
San Diego CA 8.3 B
San Jose CA 8.3 B
Denver CO 8.4 B
Tacoma WA 8.4 B
Anaheim CA 8.5 B
Fontana CA 8.5 B
Sacramento CA 8.5 B
Mesa AZ 8.6 B
Riverside CA 8.6 B
San Francisco CA 8.6 B
Spokane WA 8.6 B
Long Beach CA 8.7 B
Irving TX 8.7 B
Minneapolis MN 8.8 B
Reno NV 8.8 B
Laredo TX 8.8 B
Tucson AZ 8.9 B
Raleigh NC 8.9 B
New York NY 8.9 B
Anchorage AK 9.1 B
Chula Vista CA 9.1 B
Aurora CO 9.1 B
Bakersfield CA 9.3 C
Los Angeles CA 9.3 C
Boston MA 9.3 C
Kansas City MO 9.3 C
Virginia Beach VA 9.3 C
DesMoines IA 9.6 C
Salt Lake City UT 9.6 C
San Bernardino CA 9.7 C
Wichita KS 9.7 C
San Juan* PR 9.8 C
Honolulu HI 9.9 C
Durham NC 9.9 C
Phoenix AZ 10 C
Colorado Springs CO 10 C
Orlando FL 10 C
Charlotte NC 10 C
Oklahoma City OK 10 C
Austin TX 10 C
Glendale AZ 10.1 C
Omaha NE 10.1 C
Albuquerque NM 10.1 C
Nashville TN 10.1 C
Brownsville TX 10.1 C
Fort Worth TX 10.1 C
Fresno CA 10.2 C
Stockton CA 10.2 C
Fort Wayne IN 10.2 C
Grand Rapids MI 10.2 C
Rochester NY 10.2 C
Lexington-Fayette KY 10.3 C
North Las Vegas NV 10.3 C
Dallas TX 10.3 C
District of Columbia DC 10.4 D
Chicago IL 10.4 D
Greensboro NC 10.4 D
Toledo OH 10.4 D
Pittsburgh PA 10.4 D
Louisville KY 10.5 D
Las Vegas NV 10.5 D
Jacksonville FL 10.8 D
Indianapolis IN 10.8 D
Houston TX 10.8 D
Milwaukee WI 10.8 D
Tampa FL 10.9 D
Fayetteville NC 10.9 D
Knoxville TN 11 D
Norfolk VA 11 D
El Paso TX 11.1 D
Philadelphia PA 11.2 D
Arlington TX 11.2 D
Miami FL 11.3 D
Buffalo NY 11.4 D
Corpus Christi TX 11.4 D
Atlanta GA 11.5 F
San Antonio TX 11.5 F
Columbus OH 11.6 F
Cincinnati OH 11.8 F
Jersey City NJ 12 F
Lubbock TX 12 F
New Orleans LA 12.1 F
Baltimore MD 12.2 F
Newark NJ 12.2 F
Tulsa OK 12.4 F
St. Louis MO 12.5 F
Baton Rouge LA 13 F
Detroit MI 13 F
Birmingham AL 13.1 F
Cleveland OH 13.7 F
Memphis TN 13.7 F
Shreveport LA 18.8 F