A judge declared a mistrial in the Lindsay Clancy murder trial on Friday after jurors said they could not reach a unanimous verdict on whether she was criminally responsible for killing her three young children.

The mistrial, on the seventh day of deliberations, leaves the case unresolved and allows prosecutors to take the 36-year-old former labour and delivery nurse to trial again.

Neither Clancy, her family nor the jury showed any emotion as the judge announced the mistrial.

The deliberations took a dramatic turn late in the week when Judge William Sullivan said he was going to declare a mistrial on Friday before suddenly changing course and giving her defence lawyer a chance to appeal to the top court in Massachusetts.

The emergency appeal was quickly denied.