What does 'what' mean? (What with being so busy both at work and and at...)

[Sultano]

what is the significance of " what" in that context?
"What with being so busy both at work and and at home,she became increasingly tired and bad-tempered."

[Mister Micawber]

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what with

1. (idiomatic) Owing to; because of; as a result of.

She was sleeping very badly these days, what with the new baby and all the activity surrounding him. (Wikipedia)
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Native English teacher at Mister Micawber's