The Declining Fertility of Immigrants and Natives

From the overview:

In June 2013, former Florida Governor Jeb Bush said "Immigrants are more fertile." He and many others have argued for large-scale immigration on the grounds that America's aging society needs immigrants and their higher fertility to, in Bush's words, "rebuild the demographic pyramid." However, demographers have generally found that, although immigration can significantly increase the overall size of a nation's population, its impact on slowing the aging of American society is very limited. To the extent that immigration can impact aging, it is partly due to immigrants' higher fertility. However, immigrant fertility has declined significantly since 2008. As a result, immigration's small impact on aging is becoming even smaller.

• The birth rate for women in their reproductive years (ages 15-50) declined more than twice as much for immigrants as natives between 2008 and 2015.
   
• The birth rate for immigrant women of reproductive age declined from 76 to 60 births per thousand from 2008 to 2015 — a decline of 16 births per thousand. In contrast, native fertility declined from 55 births per thousand to 49 births per thousand — a decline of six births per thousand.
   
• Although still higher than that of natives, immigrant fertility has only a small impact on the nation's overall birth rate. The presence of immigrants raises the birth rate for all women in their reproductive years by just two births per thousand (3.6 percent).
   
• Immigration has a minor impact because the difference between immigrant and native fertility is too small to significantly change the national birth rate.
   
• Even if the number of immigrant women 15 to 50 doubled along with births to this population, it would still only raise the overall national birth rate for women by 2.5 percent.
   
• In addition to births per thousand, fertility is often measured using the total fertility rate (TFR). The TFR reports the number of children a woman can be expected to have in her lifetime based on current patterns.
   
• Like the birth rate, the TFR of immigrants has declined more rapidly than the TFR for natives since 2008. In 2008, immigrant women had a TFR of 2.75 children; by 2015 it had fallen to 2.16 — a .6-child decline. For natives it declined from 2.07 to 1.75 — a .33-child decline.
   
• Like births per thousand, the presence of immigrants in the country has only a small impact on the nation's overall TFR. In 2015, immigrants only increased the nation's overall TFR by .08 children (4.3 percent).
   
• If present trends continue, the TFR of immigrants may drop below 2.1 in the next few years, the level necessary to replace the existing population. An immigrant TFR of less than 2.1 would mean that, in the long run, immigration would add to the aging of American society.
   
• Although immigration has only a small impact on overall fertility and aging, it has a significant impact on population size. For example, new immigrants and births to immigrants between 2000 and 2015 added 30.2 million people to the country — equal to 76 percent of U.S. population growth over this time period.