The US actress announced the exciting news on Twitter last night (29 July) by posting a picture of her growing baby bump.
Sarah, who already has a son called Micah Emmanuel with her husband Peter, is wearing a green vest top and skinny jeans in the selfie and looks blooming marvellous.
Joking with her followers, Sarah commented alongside the picture: "Nope. That's not a fake belly :)"
The 33-year-old is best known for playing Dr April Kepner in the hit American medical drama Grey's Anatomy. She also starred in Everwood from 2004 to 2006.
Sarah married Peter, a university lecturer in 2002. Congratulations!
Celebrities who have announced pregnancies in 2014:
Copyright: WENN Lexie Appleby/Future Image/Bridow/Instagram