"This rule reflects a better policy, as birth tourism poses risks to national security," the State Department said. "The birth tourism industry is also rife with criminal activity, including international criminal schemes, as reflected in federal prosecutions of individuals and entities involved in that industry."

State Department officials said on a background call with reporters Thursday afternoon that consular officers have been instructed not to ask every female visa applicant whether she intends to give birth in the U.S. But if, for example, a visa applicant lists her purpose for travel as "medical reasons," she will be asked, they said. Pregnancy tests won't be part of the visa vetting process, the officials told reporters.

Pro-immigration groups immediately denounced the regulation as discriminatory and medically dangerous.

The rule will "almost certainly make it far harder for women, especially women of color, to come to the United States on tourist or business visas," said Tom Jawetz, vice president of immigration policy at the left-leaning Center for American Progress, in a prepared statement. Moreover, "by erecting new barriers to those seeking urgent medical care," Jawetz said, "the rule will also put women’s lives at risk."

The new policy is the latest step in the Trump administration's efforts to limit legal immigration to the United States.

Both as a candidate and during his tenure as president, Donald Trump railed against the practice of granting U.S. citizenship to babies born in the U.S. to non-citizen parents.

"You can't come into the country, you're illegal, you come down, you sit down, you have your baby, and we take care of the baby for the next 85 years," Trump said at the Orlando Sunshine Summit in November 2015. "The birthright citizenship, the anchor baby ... it's over, not going to happen," he added later in the speech.

The rule released Thursday, however, won't affect pregnant women who enter the U.S. illegally, because it concerns the granting of visas, a legal path to entry.

Just before the 2018 midterms, Trump suggested he might end women entering the U.S. to give birth via executive order. That raised constitutional questions about whether it would override the 14th Amendment, which states: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.”

Trump floated the idea again to reporters in August. "We're looking at that very seriously — Birthright citizenship. Where you have a baby on our land — you walk over the border, have a baby. Congratulations, the baby is now a U.S. citizen," he said last year. "It's — it’s, frankly, ridiculous."

The State Department said that it's difficult to measure precisely how many children are born to women on visitor visas, but estimated the number is in the "thousands."

The anti-immigration Center for Immigration Studies estimated that 33,000 children were born to women on tourist visas during the second half of 2016 and the first half of 2017, but the group warns that figure is "a rough approximation, based on limited data."

The 33,000 figure doesn't distinguish those women who came to the U.S. for the express purpose of giving birth — the only cohort truly categorizable as "birth tourists" — from those who merely happened to be pregnant when they arrived, or who got pregnant after they arrived.

The new State Department rule will also codify a requirement that those traveling to the U.S. for medical treatment must "establish their ability to pay all costs associated with such treatment," including travel and living costs.

Foreigners who wish to give birth at U.S. medical facilities may also be denied entry unless they can establish the birth requires "specialized medical treatment," according to the rule.

Separately, DHS also announced Thursday it is reopening the comment period on a proposal that would allow the U.S. for the first time in history to impose application fees on asylum-seekers and raise fees for certain worker visa applications.

