In the 1850s, the infant mortality rate in the United States was estimated at 216.8 per 1,000 babies born for whites and 340.0 per 1,000 for African Americans, but rates have significantly declined in the West in modern times. This declining rate has been mainly due to modern improvements in basic health care, technology, and medical advances. In the last century, the infant mortality rate has decreased by 93%. Overall, the rates have decreased drastically from 20 deaths in 1970 to 6.9 deaths in 2003 (per every 1000 live births). In 2003, the leading causes of infant mortality in the United States were congenital anomalies, disorders related to immaturity, SIDS, and maternal complications. Babies born with low birth weight increased to 8.1% while cigarette smoking during pregnancy declined to 10.2%. This reflected the amount of low birth weights concluding that 12.4% of births from smokers were low birth weights compared with 7.7% of such births from non-smokers. According to the New York Times, "the main reason for the high rate is preterm delivery, and there was a 10% increase in such births from 2000 to 2006."  Between 2007 and 2011, however, the preterm birth rate has decreased every year.  In 2011 there was a 11.73% rate of babies born before the 37th week of gestation, down from a high of 12.80% in 2006.. How many more babies were born preterm in 2006 than in 2011?