The superbitch, played by Charlie Brooks, fears she will lose the baby when she collapses in agony and starts bleeding as she weds Michael Moon (Steve John Shepherd) in Albert Square's biggest ever marriage ceremony, the Daily Star Sunday reports.
She is rushed to hospital in an ambulance, but it is unknown whether this is before or after the couple have officially wed.
An EastEnders insider said: "This is Janine's wedding so it had to be big. Ever since she inherited her gran's money she's become the most powerful and richest woman in Walford.
"Janine has spent loads on her big day, making sure everything is the best money can buy. This has left Michael feeling inferior and as we've already seen, he's turned back to his dark side.
"He's been conning money out of Jean Slater, getting her to trust him and there is lots more between these two coming up, which all comes to a head on his wedding day.
"All hell is going to break loose. There's also the small matter of Jean's niece Kat Moon coming back soon. There's no way Michael would've been able to manipulate Jean the way he has if she'd been around.
"We've already filmed the wedding and the fans can expect high drama, lots of emotion and one or two surprises. People will be shouting at their TVs for Janine not to marry Michael."
The scenes were filmed last week and will be aired at the end of next month.
Sid Owen and Sophie Lawrence, who play Janine's brother and sister, are returning for the special episodes.