Net migration from Mexico to the United States has come to a statistical standstill, stalling one of the most significant demographic trends of the last four decades.

Amid an economic downturn and increased enforcement at the U.S.-Mexico border, the number of Mexicans coming to the United States dropped significantly, while the number of those returning home increased sharply over the last several years, according to a report by the Pew Hispanic Center.

“The largest wave of immigration in history from a single country to the United States has come to a standstill,” the report says.

Between 2005 and 2010, 1.4 million Mexicans immigrated to the United States, less than half the number that migrated between 1995 and 2000. At the same time, the number of Mexicans and their children who moved to Mexico in the same five-year period rose to 1.4 million, about double the number that did so between 1995 and 2000.

The estimates are based on data from the U.S. Census Bureau and on Mexican census data. The most recent data indicate that the historic flow of migrants into the U.S. might even have started to reverse.

“We’re fairly confident that by the end of the period we were seeing more people moving to Mexico than leaving” for the United States, said co-author Jeffrey S. Passel, a senior demographer at the Pew Hispanic Center.

Illegal immigrants from Mexico residing in the U.S. still outnumber their legal counterparts, but the proportion has shifted, the report found. The number of Mexican illegal immigrants residing in the U.S. fell from 7 million in 2007 to about 6.1 million in 2011. In the same period, the number of legal immigrants from Mexico residing here increased from 5.6 million to 5.8 million.

The report attributes the changes to several factors, including the weakened economy, increased border enforcement, a rise in deportations, growing dangers at the border and a long-term decline in Mexican birthrates. Which factor is dominant is still unknown.

“At this point, it’s very hard to say because all of them are kind of working in the same direction,” Passel said.

The report comes as the Supreme Court on Wednesday is set to take up elements of Arizona’s tough crackdown on illegal immigrants, known as SB 1070. Advocates for reduced immigration cited the report as proof that tightened enforcement works. Many immigrant advocates have long cited job prospects as a primary factor in decisions to migrate.

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