Three “odd” collapses of a baby girl allegedly murdered by a nurse came “out of the blue”, a court has heard.

Lucy Letby, 32, is said to have intravenously administered air into the child’s bloodstream – causing a fatal blockage – during treatment at the Countess of Chester Hospital.

The infant, referred to as Child D, is alleged to be the third baby murdered by the defendant in a two-week period in June 2015, with another suffering a life-threatening collapse during the same time.

Jurors have heard Child D was born more than 60 hours after her mother’s waters broke and shortly after on the afternoon of June 20 2015 became “floppy” in her father’s arms.

The infant was given antibiotics some four hours later when she was transferred to the hospital’s neo-natal unit amid concerns of a suspected infection.

In the early hours of June 22 Child D suffered the first of three collapses as medics were unable to resuscitate her on the final occasion.

Giving evidence on Friday, medical expert witness Dr Sandie Bohin said she concluded Child D had contracted pneumonia before birth.

But she told Manchester Crown Court that Child D was “stable” throughout June 21 and was “improving” as she responded to appropriate treatment.

Dr Bohin said: “The thing that was striking about the collapses is that they were all sudden and unexpected. These were collapses that came out of the blue.

“She recovered pretty quickly with the first two episodes and sadly not the third.

“All the episodes were perplexing to me.

“Taking into account the suddenness of the collapses and the very quick recoveries with two of them, it was clear that this was not an infection that caused the collapses.

“It had to be something unusual and rather odd.

“So I excluded lots of other things and came to the conclusion that (Child D) had air administered to her intravenously.”

Prosecutor Nick Johnson KC asked: “Why did she recover quickly twice and die on the third occasion? Can you provide an answer to that conundrum?”

I think if the volume of air in the first two cases was small it would not be enough to kill but if a large amount when it goes to the right-side of the heart it causes a gas lock in the heart... causing the circulation to stop

Dr Bohin replied: “I can speculate. We know from animal studies with air embolus (a dose of air) it is the volume of gas and speed it is delivered that can prove fatal.

“I think if the volume of air in the first two cases was small it would not be enough to kill but if a large amount when it goes to the right-side of the heart it causes a gas lock in the heart… causing the circulation to stop.”

Ben Myers KC, defending, said: “We know whatever happened to (Child D) to cause events one and two were self-evidently not fatal and, in fact, she made a full and rapid recovery which in principle is inconsistent with air embolus, isn’t it?”

Dr Bohin said: “I don’t think it is.”

Asked what basis she had for saying how much air over a period of time would be needed for a fatality, the witness said it was based on the available literature.

Mr Myers said: “Which is based on dogs and rabbits.”

Dr Bohin said: “Yes. It is not effective to inject humans with air and see who survives and who dies.”

The witness denied she had “minimised certain facts to show how unwell (Child D) was”.

Mr Myers said: “Right from the moment of birth there is no doubt that (Child D) is very unwell.”

Dr Bohin said: “I disagree.”

Mr Myers went on: “The fatal collapse could be explained as consistent with a worsening physical condition because of an infective process.”

Dr Bohin replied: “I don’t agree with that at all.”

Letby, originally from Hereford, denies the murders of seven babies and the attempted murders of 10 others between June 2015 and June 2016.

The trial continues on Monday.