She is accused of attempting to murder the infant, Child Q, on the morning of June 25 2016 after allegedly murdering two triplets, Child O and P, on the previous two days.

The Crown says she killed them in the neonatal unit after returning from a holiday to Ibiza.

It is alleged Letby murdered seven babies in total and attempted to murder 10 others between June 2015 and June 2016.

Earlier this month in the trial at Manchester Crown Court, consultant Dr John Gibbs said the triplets' deaths were a "tipping point" with concerns about the "accumulating number of inexplicable collapses" and an "association" to Letby.

Lead neonatal consultant Dr Stephen Brearey previously told jurors he pleaded unsuccessfully to an executive to stop her from working the June 25 shift.

On Friday, the court was read a series of Facebook messages on the evening of June 25 between Letby and a registrar, who cannot be named for legal reasons.

Letby asked him: "Do I need to be worried about what Dr Gibbs was asking?"

The doctor replied: "No. He was asking to make sure that normal procedures were being carried out. What exactly did he ask?"

Letby said: "I walked into equipment room, he was asking Mary (a nurse) who was present in room and how quickly someone had gone to him as I wasn't in the room.

"He asked who was there. I said I had popped out of room but Mary was in room and Minna (another nurse) at the desk."

The doctor said: "All he was doing was checking there wasn't a delay and that a room had been left empty. There is nothing to worry about."

Letby told him she was "worried" because of her absence but said she was in the intensive care room with another baby in her care.

The doctor said: "You can't be with two babies in different nurseries at the same time, let alone predict when they're going to crash..."

Letby replied: "I know and I didn't leave him on his own. They both knew I was leaving the room. Feel better now."

The doctor said: "Nobody has accused you of neglecting a baby or causing a deterioration."

Letby said: "I know. Just worry I haven't done enough.

"We've lost two babies I was caring for and now this happened today, makes you think 'am I missing something/good enough'."

The doctor said: "Lucy, if anyone knows how hard you've worked over the last three days it's me.

"The standard of care delivered is tertiary nicu (neonatal intensive care unit) level. If *anybody* says something to you about being not good enough or performing adequately I want you to promise me that you'll give my details to provide a statement. I don't care who it is and I don't care if I've left the trust. Promise?"

Letby responded: "Well I sincerely hope I won't ever be needing a statement. But thank you, I promise."

The doctor said: "And I don't either. You'll know that the coch (Countess of Chester) mortality rate is a bit higher than the network average. It makes people (consultants) look at trends and patterns. That may have been why Dr G came to ask.

"As for the self-doubt - you have asked me this morning did I dream because I was worried about having missed something?

"No more doubt - it's not you, it's the babies. I don't know what happened to (Child O and P) and accept that the pm (post-mortem) may not give any useful answers. I do wonder if they may have had adenovirus it's terrible in neonates/perinates.

"(Child Q) is different. His behaviour is more bacterial."

Letby replies: "Thanks, really appreciate you saying that. So relieved that it's you who has been there throughout."

The doctor said: "It's true. You are one of a few nurses in the region (I've worked pretty much everywhere) that I would trust with my own children.

"If you're worried - I'm worried. You should do the APNP (advanced paediatrics) course, you'd be excellent it's true."

Letby said: "Don't know what to say. Thank you."

The doctor said: "Self doubt finished?"

Letby said: "I think so, thank you ++"

The next day, when Letby was off rota, she messaged a nursing colleague: "I worry that we've got a bug or virus or something on unit."

The colleague replied: "Would explain a lot. Hope get answers for triplets parents after how things went for (Child I)."

Letby replied: "Definitely."

Letby, originally from Hereford, denies all the allegations.

The trial continues on Monday.