A mother has been charged with involuntary manslaughter after she allegedly smothered her child while they slept next to each other.

Arissa Ward, 23, called police in Middleton, Pennsylvania, on 30 December last year after finding her infant son unresponsive on the couch next to her where they had been sleeping.

She said she had been drinking alcohol and smoking marijuana before lying on the couch next to her son, who was two months and five days old.

An autopsy carried out a week later found the child had died due to “traumatic asphyxia combined with smothering”. The coroner also found traces of marijuana in the child’s system as Ms Ward had been breastfeeding.

Ms Ward has now been charged with second-degree felony count of involuntary manslaughter and a first degree misdemeanour count of endangering the welfare of children.

Ed Marisco, Dauphin County district attorney, defended prosecuting Ward and said the baby’s death had been “caused by a reckless act”.

He said it was clear she had not meant to kill her child but "the advice from hospitals and paediatricians is pretty clear - don't sleep with your child" and that if someone is under the influence of drink or drugs "it's much more likely something like this could happen".

But Ms Ward's lawyer, Casey Shore, told Pennlive: “There's no question there was never any intention or desire to harm her child by any stretch. It's a horrible tragedy.”

He said she had one other child who was still in her custody after an investigation by child services.

Jennifer Gettle, the chief deputy district attorney, said: "I can't imagine a parent going through this.

"We had a 911 call from a mom - she is crying, she is sobbing, she is going through the realisation she has caused the death of her child."

Ms Gettle said the amount of THC – the active ingredient in marijuana – was 0.95 nanograms. She said it could have possibly made the baby more lethargic.

Mr Marisco said Ward and the child’s father, Arthur Thomas Livering, was charged with endangering the welfare of a child and possession of marijuana.

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He said the county was launching a task force to combat a rise in parents sleeping with their children in their beds.

“Our message today is don't sleep with your kid, especially if you're smoking dope or drinking all night, because you don't know what you're doing”, he added.