The Arkansas Supreme Court on Thursday overturned the conviction of a woman who was sentenced to 20 years in prison after giving birth to a baby with methamphetamine in his system.

Melissa McCann-Arms, 39, was convicted by a jury in Polk County after she and her son tested positive for meth when she gave birth at a Mena hospital in November 2012. She was convicted of a felony crime called introduction of controlled substance into body of another person.

In January, the Arkansas Court of Appeals upheld the conviction, ruling that even if the statute doesn't apply to unborn children, McCann-Arms still transferred the drug to her child in the moments between his birth and when hospital staff cut the umbilical cord.

But Arkansas' highest court reversed the conviction and dismissed the case, ruling there is no evidence McCann-Arms directly introduced methamphetamine into her baby's system by causing the child to ingest or inhale it. Likewise, there is no evidence of an ongoing transfer of methamphetamine in McCann-Arms' system after the child was born, the court ruled.

"The jury would thus have been forced to speculate that Arms was 'otherwise introducing' the drug into the child at that point," the ruling states. "When a jury reaches its conclusion by resorting to speculation or conjecture, the verdict is not supported by substantial evidence."

The court also ruled state law does not criminalize the passive bodily processes that result in a mother's use of a drug entering her unborn child's system.

"Our construction of criminal statutes is strict, and we resolve any doubts in favor of the defendant," the decision states. "The courts cannot, through construction of a statute, create a criminal offense that is not in express terms created by the Legislature."

Farah Diaz-Tello, a staff attorney with the New York-based National Advocates for Pregnant Women, had urged the court to reverse McCann-Arms' conviction and said the decision sends a message to state prosecutors about expanding the law beyond what was intended by state lawmakers.