Hayden and Ukrainian boxer Wladimir got engaged last October and announced their exciting news while taking part in the ALS Ice Bucket charity craze yesterday (20 August).
Addressing her fans in a video moments before she dunked herself in cold water, Hayden picked her nominations to do the fundraiser - and she nominated her unborn baby!
"I accept my ALS Challenge. I renominate Kacey Musgraves - you're not getting out of this, Wladimir Klitschko and my unborn child,' she said.
The Heroes actress wore a simple grey T-shirt to take part in the challenge and her rounded tummy was clear to see underneath. Aww, congratulations!
Hayden isn't the only star to announce her pregnancy using the ALS Ice Bucket Challenge.
Yesterday, Zoe Saldana finally confirmed that she is pregnant her first baby with husband Marco Perego moments before he got drenched.
Rumours have been rife that the couple are expecting a little one and Zoe proudly showed off her tummy while chatting in their video.
Wow, we wonder who will be next?!
Celebrities who have announced pregnancies in 2014:
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