Her defenders said she had suffered a miscarriage.
Salvadoran authorities said the woman carried her baby to near-full term and gave birth in June 2020.Â
After having the baby, she stabbed it in the neck six times, they said.
The Citizen Group for the Decriminalisation of Abortion, a feminist non-governmental organisation that defended the woman, said in a report on Monday she had suffered a miscarriage in the bathroom of her home while five months pregnant.
Morena Herrera, head of the NGO, told Reuters the woman, identified only as Lesli, had tried to cut the umbilical cord herself after the miscarriage, but it was dark and her home had no electricity.
El Salvador has some of the world's harshest anti-abortion laws, which ban all kinds of terminations even if the pregnancy poses a risk to the mother's life or results from rape or incest.
The Salvadoran government did not respond to a request for comment.
"It is not the first time that the prosecution has constructed a story that totally criminalises women," Herrera said.
According to the Citizen Group for the Decriminalisation of Abortion, four women are imprisoned and another five have been charged in El Salvador in similar cases.
