Analysis of birth records shows that in 2002 almost one in four births in the United States was to an immigrant mother, legal and illegal, the highest level in American history. The enormous number and proportion of children from immigrant families may overwhelm the assimilation process, making it difficult to integrate these new second-generation Americans. At present, the U.S. government automatically gives American citizenship to all people born in the country, even the children of tourists and illegal aliens.

Among the study’s findings:

• In 2002, 23 percent of all births in the United States were to immigrant mothers (legal or illegal), compared to 15 percent in 1990, 9 percent in 1980, and 6 percent in 1970.

• Even at the peak of the last great wave of immigration in 1910, births to immigrant mothers accounted for a slightly smaller share than today. After 1910 immigration was reduced, but current immigration continues at record levels, thus births to immigrants will continue to increase.

• Our best estimate is that 383,000 or 42 percent of births to immigrants are to illegal alien mothers. Births to illegals now account for nearly one out of every 10 births in the United States.

• The large number of births to illegals shows that the longer illegal immigration is allowed to persist, the harder the problem is to solve. Because as U.S. citizens these children can stay permanently, their citizenship can prevent a parent’s deportation, and once adults they can sponsor their parents for permanent residence.

• The large number of children born to illegals also shows that a “temporary” worker program is unrealistic because it would result in hundreds of thousands of permanent additions to the U.S. population each year, exactly what such a program is suppose to avoid.

• Overall, immigrant mothers are much less educated than native mothers. In 2002, 39 percent of immigrant mothers lacked a high school education, compared to 17 percent of native mothers. And immigrants now account for 41 percent of births to mothers without a high school degree.

• The dramatic growth in births to immigrants has been accompanied by a decline in diversity. In 1970, the top country for immigrant births — Mexico — accounted for 24 percent of births to immigrants, by 2002 it was 45 percent...