Federal agents walk past the Carlyle Apartments, the location of a suspected "baby tourism" operation, in Irvine California March 3, 2015. [Photo/Agencies]

LOS ANGELES - At least some of the pregnant women from China caught up in raids this week on so-called maternity hotels, catering to foreign mothers-to-be seeking US citizenship for their babies, are still likely to remain long enough in California to give birth on American soil.

That's because US immigration officials investigating "Chinese birthing houses" for alleged visa fraud, tax evasion and money laundering hope to coax their clients into providing testimony and evidence against operators of those businesses.

Federal officials have declined to say how many pregnant customers they encountered in searches conducted on Tuesday of more than 50 locations suspected of involvement in three large "maternity tourism" networks in Southern California.

No arrests have been made as of Thursday, said Virginia Kice, a spokeswoman for the US Immigration and Customs Enforcement agency, or ICE.

Instead, paying customers of the apartment houses raided in the sweep were taken in for initial interviews by immigration agents, who confiscated their passports and "referred them for more questioning," Kice said.

She declined to say how many if any of the women would end up staying long enough to give birth in the United States now that the schemes were exposed but suggested some were likely to remain in California as the investigation progresses.