Rates of preterm births and births in teenagers have decreased in the United States from 2007 to 2014, according to a study in the CDC’s Morbidity and Mortality Weekly Report. The study also found that preterm births were more common among the youngest and oldest mothers.

Researchers used National Vital Statistics System data for live births to U.S. residents to analyze the effects of maternal age on the decline in preterm birth rates. Preterm births were defined as less than 37 weeks of gestation, and maternal age was categorized as ≤19, 20 to 24, 25 to 29, 30 to 34 years of age, and ≥35 years of age. The researchers examined changes in maternal age distribution and the change in age-specific preterm birth rates.

Maternal age increased from 27.4 years to 28.3 years between 2007 and 2014. The researchers observed a decrease in the percentage of births to mothers younger than 24 years of age. There was also a 39.5% decrease in births to teens and an increase in births to women older than 25 years of age.

Continue Reading

The overall preterm birth rate decreased from 10.41% to 9.54% between 2007 and 2014. The decrease in preterm birth rates was observed for all mothers younger42 years of age, and the absolute rate difference was highest among teens and lowest among women who were at least 35 years of age.

Among women who were younger than 19 years of age and for women between 20 and 24 years of age, the change in age distribution had a larger effect than in the change in age-specific preterm birth rate on the overall preterm birth rate decline. For women between 25 and 29 years of age, the effect of both components contributed to the overall preterm birth rate decline, but the effects of both components among women greater than 30 years of age did not contribute to the overall decline.

“The overall decline in the preterm birth rate from 2007 to 2014 is related in part to the changing maternal age distribution associated with the success of teen pregnancy prevention and declines in unintended pregnancy,” the authors noted.

“Prevention of unintended pregnancy and encouragement of optimal birth spacing is one part of a five-part strategy for preterm birth prevention. Other strategies include improved access to preconception care, preterm birth risk identification and treatment, reduction of elective delivery before 39 weeks gestation, and single embryo transfer in assisted reproductive technology. These strategies need to be implemented throughout the reproductive life span to reduce preterm births for all maternal ages.”


  1. Ferre C, Callaghan W, Olson C, et al. Effects of maternal age and age-specific preterm birth rates on overall preterm birth rates—United States, 2007 and 2014. MMWR. 2016;65(43):1181-1184. doi:10.15585/mmwr.mm6543a1.