More than 5,000 pregnant Russian women have entered Argentina in recent months, including 33 on a single flight on Thursday, officials say.
The latest arrivals were all in the final weeks of pregnancy, according to the national migration agency.
It is believed the women want to make sure their babies are born in Argentina to obtain Argentinian citizenship.
The number of arrivals has increased recently, which local media suggests is a result of the war in Ukraine.
Of the 33 women who arrived in the Argentinian capital on one flight on Thursday, three were detained because of “problems with their documentation”, joining three more who arrived the previous day, migration agency head Florencia Carignano told La Nacion.
The Russian women had initially claimed they were visiting Argentina as tourists, she said.
“In these cases it was detected that they did not come here to engage in tourism activities. They acknowledged it themselves.”
She said the Russian women wanted their children to have Argentinian citizenship because it gave more freedom than a Russian passport.
“The problem is that they come to Argentina, sign up their children as Argentinean and leave. Our passport is very secure across the world. It allows [passport-holders] to enter 171 countries visa-free,” Ms Carignano said.
Having an Argentine child also speeds up the citizenship process for parents. As it stands, Russians can travel visa-free to only 87 countries.
Travel to many Western countries has become more difficult for Russians since their country invaded Ukraine last February.
Last September, the visa facilitation agreement between the EU and Russia was suspended, resulting in the need for additional documentation, increased processing times and more restrictive rules for the issuing of visas.