A French court has jailed a woman for nine years for killing eight of her newborn babies, after a harrowing trial in which she lied about having had an incestuous relationship with her father.

Dominique Cottrez, a 51-year-old former health worker, was found guilty of suffocating eight of her babies shortly after secretly giving birth to them between 1989 and 2000. Most of the killings occurred in the bathroom of her home near the Belgian border.

The sentence was half that requested by prosecutors. After five hours of deliberation, the jury said Cottrez suffered from impaired judgment. Visibly relieved at the verdict, Cottrez embraced her husband and two daughters.

Her lawyers had pleaded with the nine-member jury to take into account the “distress” of a fragile woman plagued by neuroses. “If this women took pleasure [in her acts] we would not have found the bodies. She conserved them … she woke up at night in winter to cover their bodies,” said lawyer Frank Berton.

Another lawyer, Marie-Hélėne Carlier, recalled that other countries such as Finland, Switzerland and the UK had often reduced the prison sentences of women who killed newborns after pregnancy denial.

Carlier said Cottrez had been “destroyed” after a midwife chided her for being overweight during the birth of her first child. “We never pleaded innocence, only distress,” Carlier said.

Cottrez’s crimes were uncovered in July 2010 when the new owner of her parents’ former home in northern France unearthed the bodies of two of her infants wrapped in plastic bags buried in the garden. A police investigation turned up six other tiny corpses in a tank in the garage at Cottrez’s home.

The housewife initially told investigators that she had feared the babies were born from a sexual relationship with her father that had taken place from her childhood until his death in 2007.

However, testing showed her husband had fathered the children and, in a spectacular turnaround, on Monday she admitted in court that she had fabricated the story.

Cottrez was able to hide the pregnancies from her doctors as well as her husband and two adult daughters in part due to her obesity. She weighed up to 130kg (20st) while pregnant.

“I did all this alone, I admit it,” she told the court on Wednesday, though she added she believed her husband had been aware of what was happening.

The magistrate Annelise Cau said the killings had been carried out with “determination, awareness, organisation and above all cool-headedness”.

The prosecutor Eric Vaillant said Cottrez needed to go to prison “so that she realises the absolute horror of the crimes she has committed”.