Sylvie Horning admitted to strangling five children after giving birth to them (Representational)

French prosecutors on Thursday demanded a 20-year prison term for a woman charged with killing five of her children right after they were born, a crime that only came to light one and a half decades after the corpses were discovered.

Sylvie Horning, 55, was detained in November 2017 on suspicions she murdered the five children between 1990 and 2005.

Horning, the mother of three adult children, is thought to have hidden her pregnancies even from her partner, giving birth in secret and then strangling the newborns at her house in Wittelsheim in eastern France.

Nothing untoward was suspected until the discovery in 2003 of the bodies of four babies in rubbish bags in the nearby Galfingue forest.

But the initial investigation was closed in 2009 after it failed to yield clues to the deaths.

It was reopened in 2016 to take advantage of advances in DNA testing, and a year later investigators made the first link between Horning and the deaths, completely by chance, after her DNA was taken in separate case following a fight with neighbours.

This then showed that she was the mother of the children whose corpses were found.

Horning admitted to strangling five children after giving birth to them in secret in a bathroom. A fifth baby was then found in a freezer at her home.

Her partner, who died in 2018, had said he was completely unaware of the events. Horning's mother is still alive but did not testify at the trial for health reasons.

Prosecutor Melody Barbuti said she was asking for 20 years in jail rather than a life sentence, given the possibility that Horning could be reintegrated with society.

She told the court in the eastern town of Colmar that the trial has shown Horning "did not love these babies, she considered them as things".

Horning remained immobile in the defendant's box during the hearings, her voice only breaking with emotion when she described abuse as a child.

Her three grown-up children -- a son and two daughters who have renounced their mother -- were present in court.

"I will accept all the sentences, even if it is 30 years in prison. If I was told 'you die tonight', I would accept it immediately," Horning said in court on Wednesday.

She claimed that the children "were not babies for me but beings that my body and spirit did not accept."

The trial opened on Tuesday, and a verdict is expected later on Thursday.