More Americans were born in 2007 than in any other year in history. According to preliminary data from the National Center for Health Statistics, births topped the previous record of 1957, at the height of the baby boom. Birth rates have been inching up in recent years, for reasons that are not entirely clear. Women living in the U.S. in 2007 will have an average 2.1 children over their lifetimes, a number that demographers consider the bare minimum to sustain population levels without immigration. In addition, U.S. women are having far fewer babies than in the 1950s—before the birth-control pill became available—when the average was nearly four children per woman. But the population is almost twice as large now, which is the main reason behind the record-breaking number of births.

U.S. IN 1957

Population: 171 million

Births: 4,308,000

Births per 1,000 women ages 15 to 44: 122

U.S. IN 2007

Population: 301 million

Births: 4,317,119

Births per 1,000 women ages 15 to 44: 69

Population numbers are U.S. Census Bureau estimates:; NCHS reports are available at