China, Taiwan and Russia are expected to be hard hit by a new Trump administration crackdown on pregnant foreigners traveling to the United States ostensibly to give birth. The crackdown takes effect January 24 but the official announcement about it was only sent to U.S. embassies around the world on January 22.

This practice of giving birth in the U.S called birth tourism by the Americans, results in a baby automatically obtaining U.S. citizenship under the 14th Amendment. President Donald Trump, who holds anti-immigrant and racist views, has constantly criticized it. These three countries are among the leaders in birth tourism in the U.S.

The U.S. National Center for Health Statistics (NCHS) estimates there were 7,462 births to foreign residents in the United States in 2008, the most recent year for which statistics are available. Pregnant women from China and Taiwan prefer to give birth in California and Saipan (a U.S. territory), while Russians prefer Florida. U.S. politicians refer to babies born this way as "anchor babies."

The U.S. Department of State said the new rules would take effect January 24. On Thursday, the Trump White House said the State Department "will no longer issue temporary visitor (B-1/B-2) visas to aliens seeking to enter the United States for birth tourism."

These women will be denied temporary visas if it's found the "primary purpose" of travel is to obtain U.S. citizenship for a child by giving birth in the United States, says an amended State Department regulation to be published Friday.

The rule, however, applies mainly to Asian countries such as China but doesn't apply to 39 countries -- most of which are in Europe. The State Department said these exempt countries are part of the Visa Waiver Program. This program allows citizens of specific countries to travel to the U.S. for tourism, business, or while in transit for up to 90 days without having to obtain a visa. The program includes the UK, Australia, Japan, South Korea and almost all member states of the European Union (EU).

The State Department, however, hasn't been able to explain how it will accurately determine if a pregnant woman intentionally wants to give birth in the U.S. It might well be a pregnant woman travels to the U.S. on business or to visit relatives and then gives birth. The State Department also hasn't been able to explain the specific ways the new rule will be enforced. Consular officers were told they couldn't directly ask a woman if they're pregnant.

"You must not ask a visa applicant whether they are pregnant unless you have a specific particularly reason to believe they may be pregnant and planning to give birth in the United States," said the State Department's memo to U.S. embassies seen by CNN. "You should document any such reason in your case notes. You must not, as a matter of course, ask all female applicants (or any specific sub-sets of applicants) whether they are pregnant or intend to become pregnant."

A State Department official said the "specific particularly reason" for bringing the topic up could be if an applicant says she'll be traveling for a medical procedure, which is one of the options already on the application.

The official said a reply like this would trigger more intrusive questioning of the applicant. He said consular officers aren't allowed to require a pregnancy test. Trump's State Department does "not believe that visiting the US for the primary purpose of obtaining U.S. citizenship" for a child "is a legitimate activity."