Cristy Proctor, 40, from Illinois, said she wants people to understand they shouldn't fear a Down's syndrome diagnosis.
Reflecting on her own experience with her daughter Isabella, now 21 months old, Proctor said she wants expectant mothers who may be going through this to focus on the positives.
"Two years ago today, I found out my baby would be born a girl. The news was quickly followed with the diagnosis of Down syndrome," Proctor wrote on Facebook.
"I spent much of my remaining pregnancy in worry, fear of the unknown and probably every of emotion you can think of and it was a very sad time for me."
"As hard as it may be to do, focus on your exciting news of simply having a baby. What a joyful celebration," Proctor wrote alongside a photo of her daughter's scan.
"It is a time for you to fall in love with a child you've not even met yet.
"It's a time to prepare a nursery and pick out names. It's a time to be cherished with your family. Everything else will come in time.
"I tell you this as an encouragement to those that may have just received the same news."
Proctor posted the message on 4 April 2016 and it was liked by more than 700 people in two days.
She said reading inspiring stories after finding out about Isabella's diagnosis really helped her, which was why she decided to share her story.
"People with Down's syndrome do live normal lives, just like anybody else," she told ABC News.
"Do we have struggles? Absolutely. If one child is saved because of our story, it makes everything worth it."
Proctor's daughter has a dedicated Facebook page, Isabella 'Amazing' Grace - My Down syndrome Journey, with more than 21,000 followers.