Abortion is illegal in Peru except in cases when the life of the mother is directly at risk. So that was not an option for this woman and she agreed to hand her child over in exchange for the equivalent of around $1,200, officials said.

Jorge Chavez Cotrina, the coordinating prosecutor for the state attorney’s office in Lima specializing in organized crime, said the group likely targeted poor women in desperate straits.

He said the traffickers “went to these places that exist in different cities where they perform abortions” and offered to pay women to have the babies and give them up, or approached destitute women who were in the last months of their pregnancy and offered to pay for their expenses in exchange for the child. Prosecutors suspect two other children had been recently sold.

He also said that the biological parents of the baby taken into custody have been detained for selling their daughter.

“Being in an economic crisis, these women are more easily convinced,” Mr. Cotrina said.

The arrests came a day before the American Embassy in Lima held an event highlighting a new program in which the United States and Peru would cooperate to provide protections for vulnerable women and children in an effort to prevent them from becoming victims of trafficking.

Elvia Barrios Alvarado, a Supreme Court judge, said the country’s judicial system is committed to holding human traffickers accountable and highlighted the disproportionate toll that trafficking takes on women.

“Its main victims are women,” she said. If victims do not find support, “if they collide with an adverse judicial decision, the lack of confidence in justice will favor the business of traffickers and impunity to perpetuate this type of crime.”