Another important factor affecting infant mortality differences is the percentage of infants born preterm (i.e., before 37 completed weeks of gestation), because preterm infants have higher mortality rates than those born at 37 weeks of gestation or more (14). In 2010, after births at less than 24 weeks were excluded, 9.8% of U.S. births were preterm,the highest among the 19 countries studied (Figure 3). The percentage of preterm births in the United States was 40% higher than in England and Wales, and 69%–75% higher than in Finland, Ireland, and Sweden.