Trump supporters protest outside the Luxe Hotel, where Republican presidential candidate Donald Trump was expected to speak in Brentwood, Los Angeles, California, United States July 10, 2015. Reuters

Undocumented immigrants are having fewer children, a report published Friday by the Pew Research Center found. Roughly 295,000 children were born to unauthorized-immigrant parents in 2013, representing roughly 8 percent of the 3.9 million U.S. births that year. In 2007, undocumented immigrants had 370,000 babies, or about 9 percent of all U.S. births.

The new data comes amid a national debate on birthright citizenship. Some Republican presidential contenders, including frontrunner Donald Trump, have proposed overhauling the 14th Amendment of the U.S. Constitution that grants automatic citizenship to anyone born in the United States. "This remains the biggest magnet for illegal immigration," Trump has said.

Roughly 11.3 million unauthorized immigrants lived in the U.S. in March 2013. They make up about 4 percent of the total population, but tend to have higher birthrates than other groups living in the U.S. In general, women across the United States are having fewer children, with the nation’s birth rate hitting a record low in 2013. White mothers had 2.9 million babies in 2013, while black mothers had 634,760 children that year.

In 2012, there were 4.5 million U.S.-born children living with at least one parent without legal permission to live in the country. Overall, about 38 percent of undocumented immigrants live with their U.S.-born children.

Most undocumented immigrants in the U.S., or about 5.8 million, originate from Mexico. Another 1.4 million arrived from Asia, the Washington Post reported.

Legal immigration has also fueled the nation's increasingly diverse population. In 2012, 16 percent of the adult population in the United States was first generation and 8.4 percent was second generation.

Americans largely support immigration reform policies that would allow undocumented immigrants to obtain more legal rights. Roughly 72 percent of Americans said they would support allowing undocumented immigrants currently living in the U.S. to stay legally if they meet certain requirements, according to a Pew Research Center poll conducted in May. Roughly 56 percent of Republicans supported such a stance, while 80 percent of Democrats backed an immigration overhaul.