Population changes are a key factor influencing birth patterns in recent decades. There are fewer women in the prime childbearing years now than in 1990, as the youngest members of the giant Baby Boom generation have aged into their mid-40s. But changes in the race and ethnic makeup of young women — chiefly, the growth of the Hispanic population, which has higher birth rates than other groups — have helped keep birth numbers relatively level.
Another influence on births is the nation’s growing number of immigrants, who tend to have higher birth rates than the native born (although those rates have declined in recent years). The share of births to foreign-born mothers, 15% of U.S. births in 1990, has grown at least 60% through 2004. Births to foreign-born women in 2004 accounted for the majority of Hispanic (61%) and Asian (83%) births.
According to Pew Research Center population projections, 82% of the nation’s population growth through 2050 will be accounted for by immigrants who arrived in the U.S. after 2005 and their descendants, assuming current trends continue. Of the 142 million people added to the population from 2005 to 2050, according to the projections, 50 million will be the children or grandchildren of new immigrants.