TORONTO - Mothers who kill their babies can be convicted of infanticide instead of murder, Ontario's highest court ruled Wednesday, though it said whether that law is still medically and socially relevant is up to Parliament.

The Court of Appeal for Ontario ruling is the first time a Canadian appellate court has examined in detail provisions in the Criminal Code that have long caused uncertainty, the court said.

The court was asked to consider the law in a case of a woman who was convicted of infanticide for killing two of her young children, even though the Crown proved the case had the essential elements of first-degree murder.

In appealing that decision, the Crown argued the wording of the law means a woman charged with murder could only be found guilty of infanticide if the elements of murder were not proven.

Infanticide is defined as a woman wilfully killing her newborn child when her mind is disturbed as a result of childbirth or lactation and carries a maximum five-year sentence, as opposed to a life sentence for murder.

When the law was first introduced in 1948, the death penalty was mandatory for all murders and Canadian juries were reluctant to send the often poor, young and emotionally distraught women to their deaths, the court said.

In this case, the Crown argued the concept of infanticide relies on discredited medical opinions and assumptions about the plight of young, unwed mothers that no longer hold true.

However, "it is not for the court to decide whether that partial defence reflects sound criminal law policy or should be reconsidered in light of advancements in medical knowledge and/or changed social circumstances," the court said in its ruling.

"Those are matters for Parliament."

The intent of Parliament in 1948 was to both create a separate offence of infanticide and a partial defence to murder, the court ruled. It said that while some might argue amendments six years later softened the language in the law, the intent was the same.

Justice David Doherty, writing for the unanimous three-judge panel, set out an approach to be taken in cases where infanticide is advanced as a defence for murder.

If the judge or jury decides the accused committed a homicide, they should first consider infanticide. If the elements of infanticide are met beyond a reasonable doubt, the woman must be found not guilty of murder but guilty of infanticide.

The woman at the centre of this case, known as L.B., was 16 when she decided to get pregnant with her boyfriend, the Crown said. She smothered the baby at 10 months old and four years later she smothered another one of her babies at about two months old.

The deaths were attributed at the time to Sudden Infant Death Syndrome and L.B. only confessed years later. She was sentenced to spend one year in prison after the judge accounted for pre-trial custody.