Harold's character Lola Pearce - Billy Mitchell's granddaughter - will give birth next Monday (July 23) in scenes to be aired live on BBC One.
She confessed to What's on TV regarding the challenge: "I'm terrified! I'd rather have a baby in real life than do this live!"
However, the star added: "But it's a once-in-a-lifetime opportunity and it is nice of them to trust me with it.
"We've already filmed the lead-up to the birth and I was knackered after screaming and crying and pretending to push all day."
Speaking to Digital Spy recently, Harold stated her belief that she has improved as an actress since joining the soap.
Meanwhile, Perry Fenwick - who plays Billy - displayed similar apprehension earlier this month over his live Olympics torch run.
> Read our recent interview with EastEnders actor Perry Fenwick here Get the Inside Soap magazine on your iPhone or iPad