Many pregnant women in the U.S., particularly in the South, face inadequate prenatal care, complicated by abortion restrictions, air pollution and extreme heat, according to a new March of Dimes report. As a result, there have been no improvements in the preterm birth rate in the last 10 years, NBC News reports. In its annual report, released Thursday, the March of Dimes gave the U.S. a dismal D+ grade based on the number of babies born too soon last year. Last year, the preterm birth rate was 10.4%. In 2022, it was 10.5%. In fact, little has changed in the past decade. In 2013, the preterm birth rate was 9.8%. “It’s really frustrating,” said Dr. Sarahn Wheeler, a maternal-fetal medicine specialist at Duke University Medical Center in Durham, North Carolina. “I take care of patients who are the real human stories behind the numbers.” Wheeler was not involved with the March of Dimes report. About 370,000 babies were born at 37 weeks’ gestation or earlier last year, according to the report. Preemies are often at higher risk for physical or intellectual disabilities. The problem is particularly troublesome in areas of the country without doctors, nurses, midwives or medical centers specializing in maternity care. They include states in the South with the most preterm births, according to the report: Alabama, Arkansas, Georgia, Louisiana, Mississippi and South Carolina. “Inadequate prenatal care has reached its highest level in a decade to an alarming 15.7%,” said Dr. Amanda Williams, interim chief medical officer at the March of Dimes. External factors in premature births also play a role, the March of Dimes suggested. More than 40% of pregnant people were exposed to extreme heat, and nearly three-quarters lived in areas with poor air quality, the report found. Abortion Nov 10 Study maps how nonprofit religious groups set up facilities near abortion clinics Abortion Aug 1 Some OB-GYNs aren't getting abortion training, report finds, while pregnancy complications are on the rise Health Jul 1 Moms are going viral for sharing dramatic before-and-after photos of ‘pregnancy nose' “There is an increasing recognition that things like climate change” have a significant impact on preterm births, Wheeler said. Chronic health conditions among mothers are another significant factor. Women with diabetes had a preterm birth rate of 28.8%, and it was nearly the same, 23.3%, among women who had high blood pressure. Experts worry the problem could worsen as pregnant women increasingly go without doctors’ care amid an exodus of OB-GYNs in states with strict abortion bans. “We can’t ignore the data that tells us that there are more hospitals closing, that there are OB/GYNs who are retiring early and fewer medical students going into OB/GYN in states that have the strictest abortion bans,” Williams said. Taken together, Wheeler said, the research “underscores the need for a real commitment for the research to understand preterm birth as a disease process to offer better therapies and better hope for these families.” This story first appeared on NBCNews.com. More from NBC News: Elon Musk’s new ‘department’ seeks ‘super high-IQ’ staff for unpaid jobs David Lynch says he began smoking at age 8, now needs supplemental oxygen for most activities 10-year-old walks alone a mile away from Georgia home, leading to his mother’s arrest