"The pimps would let prostitutes who fell pregnant have the babies, which is something new because usually they force the women to have an abortion," Ewa Olkiewicz, spokeswoman for the police in the western Polish city of Poznan, told AFP.

The women were forced to continue working until their pregnancies were visible, according to a report in the Polish newspaper Gazeta Wyborcza quoted by news agency DPA. They were then taken to a clinic in Germany to give birth. The women received a small sum of money for the babies, who were then solc.

The five suspects, one of whom was a policeman, were arrested in the western town of Gniezno after one of the women filed a formal complaint against the gang, Olkiewicz said.

Polish police have apparently teamed up with their German colleagues to track down the buyers.