Authorities in San Gabriel, Calif., recently shut down a makeshift maternity center for pregnant Asian tourists. The expectant moms, many from wealthy backgrounds, allegedly wanted to give birth on American soil, so their babies would be U.S. citizens. Is this an isolated case, or is "maternity tourism" a serious immigration problem? Here, a brief guide:

How did this operation work?
The women, most of them from wealthy families in China and Taiwan, acquired legitimate tourist visas. They paid $25,000 to $35,000 to fly to the U.S. and stay in the unlicensed maternity center. They then gave birth at local hospitals, and returned to the center before traveling home. The facility was set up in three condominiums on a palm-tree lined residential street, presumably to avoid attracting attention.

So how'd they get caught?
For months, people in the suburban Los Angeles neighborhood had noticed numerous pregnant Asian women coming and going from the upscale townhouses, at all hours. After receiving complaints, government inspectors visited and found 12 Chinese women, and 10 newborns in clear plastic bassinets in a kitchen converted to a nursery.

Were they arrested?
No. The women weren't taken into custody — none had obtained a visa fraudulently. But the center was shuttered because walls had been knocked down to connect the apartments, which violated building codes and made the structure unsafe.

Is this a common problem?
No one knows how many pregnant women enter the country each year with the express purpose of acquiring citizenship for their newborns. Jon Feere, a legal policy analyst at the Center for Immigration Studies, makes a rough estimate that 40,000 children are born to maternity tourists each year. The number appears to be on the rise, however. Births to non-resident mothers in the U.S. rose by 53 percent between 2000 and 2010, while total births rose by just 5 percent.

Haven't I heard congressmen debating this issue?
Yes. Many Republicans have been warning for months of "anchor babies," and some, like Rep. Louie Gohmert (R-Texas), have suggested that terrorists might use this citizenship loophole as part of a decades-long plan to secure easier access to the U.S. As such, there's been a big push among conservatives to rollback the 14th Amendment, which guarantees "birthright citizenship" for any baby born in the U.S., though others warn that doing so would create a system in which some babies are born without citizenship to any country. Rep. Judy Chu (D-Calif.) says maternity tourism is far too rare to be a justification for eliminating birthright citizenship. "The 14th Amendment is fundamental to the U.S.," she said, as quoted by the Associated Press, "and too important to change because of the practice of a few."

Sources: Associated Press, LA Times, Pasadena Star-News, The Daily, San Gabriel Valley Tribune, Mother Jones