Three doctors and a nurse have been arrested for allegedly selling newborns after telling mothers their babies had died at a private hospital in Mexico City, authorities said Wednesday.

Police uncovered the scheme after one of the women learned her baby was alive and had been sold to another woman for 15,000 pesos ($1,130), said Luis Genaro, the capital's deputy attorney general.

The woman gave birth to a girl through cesarean section at the Central West Hospital in a working-class district in October 2008, Genaro said at a news conference.

He said she told authorities she heard her baby cry but when she asked to see the child, doctors told her she had to wait until the effects of the anesthetics wore off. Later, doctors told her the baby had been taken to another hospital. A day later, the woman was told her baby died and had been cremated, Genaro said.

The woman learned the truth from an-email sent to her by a man believed to be the son of the hospital director, Genaro said.

The woman accused of buying the newborn has been arrested. Three doctors, a nurse and a receptionist from the hospital are also in custody.

Genaro said police believe the group sold several newborn babies but have not yet determined how many. They face charges of trafficking in minors, organized crime and falsifying documents.

He said a married couple has also been arrested for allegedly paying the hospital to falsify a birth certificate for a baby that the pair had been given.

In a report this year, the U.S. State Department described Mexico as "a large source, transit and destination country" for human trafficking. The majority of victims are undocumented migrants and women and children trafficked for sexual exploitation, according to the 2009 Trafficking in Persons report, which studied the problem worldwide.

The report said that although Mexico was stepping up efforts to crack down, convictions against human traffickers remain rare. The report said no trafficking offenders were convicted in Mexico in 2008.