Preterm Birth by Gestational Age (IMAGE) March of Dimes Foundation Caption Of the 520,000 babies born preterm each year, about 80 percent are considered "late preterm," defined at birth between 34-36 weeks gestation. Credit CDC/NCHS, National Vital Statistics System Usage Restrictions Please credit the March of Dimes License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.