Police in the southern Indian city of Hyderabad have arrested four people in connection with an alleged attempt to swap a baby girl for a boy.
Three of those held are employees of the Nayapul Government Maternity Hospital.
Nazeer Ahmed, the father of the baby girl, was also arrested and has appeared in a court in the city.
Both infants involved in the incident were reunited with their families on Monday.
Correspondents say the case underlines the continuing preference of many Indian parents for male children in a society which widely sees boys as future breadwinners, but girls as a financial burden.
Additional Commissioner of Police Abdul Khayyum Khan told the BBC the three hospital employees are accused of criminal negligence, endangering the life of a baby and the alteration and creation of false records.
The employees are believed to be responsible for handing over the newborn son of Latha Reddy to Mehmooda Bi on 20 April.
The baby girl is now with her mother
Hospital sources say the workers have been suspended.
Mr Ahmed and a fifth person, who has not been arrested, face charges of impersonating the boy's biological parents and concealment of evidence.
After appearing in court, all the accused were remanded to custody for 15 days.
The arrests come a day after the missing baby boy was reunited with his parents, Latha and Janga Reddy, after 21 days.
"I felt as if this is the rebirth of my son after his death," Mrs Reddy told the BBC on Monday.
Although baby swapping has not previously been reported in this part of India, Hyderabad was recently the centre of a major racket which saw poor parents selling their babies for adoption.
We did not know that the police were looking for this baby boy
But the additional commissioner of police said investigations did not indicate that any exchange of money had taken place during the swap.
"The family which was given the male child in place of the female baby is too poor to pay any money," he said.
Mehmooda Bi said that she and her husband had been forced to take away the male child by the hospital despite their objections.
But the police say that despite knowing that the boy was not theirs, the couple remained silent for three weeks and tried to conceal the facts.
Mehmooda's family had previously named the newborn boy Shaikh Maaz Ahmad.
But now his natural parents have renamed him Hanumantha Reddy, after the Hindu god Hanuman.