Chief Justice Ewan Crawford yesterday declared the charges against Kylie Marie Parker, 25, could not be proven because the prosecution had failed to present sufficient evidence.

Prosecutor Peter Sheriff had alleged that Ms Parker failed to seek immediate medical treatment for her baby's broken arm.

But Chief Justice Crawford told the jury that allegation was not supported.

``There's absolutely no evidence that there was any injury to the child's arm earlier than that day,'' he said.

The jury sat through three hours of the prosecution case yesterday before Chief Justice Crawford directed them to find Ms Parker not guilty.

The court heard Ms Parker's then-partner, Stephen Edward Palmer, 30, called an ambulance to their Pioneer Parade home at 5.22am on December 22, 2010.

In it, Palmer told the ambulance officer he, ``laid (the baby) down and I didn't see where her arm was, and she just laid on it''.

``I think it just twisted behind her . . . it wasn't me,'' he said.

The baby's cries could be heard in the background.

Paediatrician Dr Ingrid Ells examined the baby at the Launceston General Hospital that morning and said her upper left arm was swollen with a ``visible bend''.

Speaking from the witness box this morning, Dr Ells said the baby had a spiral fracture to her upper left arm and two chips to the bones of her forearm.

She said shadows on the X-ray meant the fracture may have occurred up to 10 days ago but could also have occurred that morning.

Defence counsel Tamara Jago argued the evidence, including that of a child health nurse who performed a full examination of the baby just days before the baby was taken to hospital, supported Ms Parker's claim that they had called the hospital straight away.

Palmer pleaded guilty on Monday to the ill-treatment of a child and will face court for sentencing submissions today.