The actress, who plays Fiz Brown in the ITV soap, announced her happy baby news via Twitter on Wednesday afternoon (21 May).
Jennie wrote: "We have some news to share. Chris and I are expecting an addition to our family. Very happy x."
Among those sending congratulations was co-star Jack P Shepherd, who welcomed son Reuben in December.
"Knew it!" he tweeted. "Well done!"
Jennie and restaurant manager Chris have been together since 2005. Last year, the actress admitted that she hadn't got time for marriage or babies.
"I haven't got time - for babies or marriage. I don't like being the centre of attention so a big wedding isn't for me."
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Stars who announced pregnancies in 2014 in pictures:
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