But shortly after her order went "into production", Ms Egan received a phone call from her doctor.
"Great news," she was told. "We went ahead and upgraded you to extra chromosomes for free! You'll receive the extra chromosomes with your completed order in 9 months."
I was mad, Ms Egan explains. "All the other orders I had seen displayed via perfect Instagram posts did NOT have extra chromosomes." And yet, she continues, "I decided that receiving my order with extra chromosomes was better than not receiving an order at all, so I settled in to wait for this surprise upgrade to arrive."
And when she did, Ms Egan couldn't have been more delighted.
"I have now had my order for two months and am writing this review to let others know the upgrade to extra chromosomes is amazing!!" She writes. "If offered, definitely take it!"
Sharing some beautiful photos of her baby girl Gwendolyn, her "finished product", Ms Egan writes, "you can see the extra chromosome is so worth it - it is extra cute, extra special, and extra-ordinary! So much extra joy.
"Would purchase again for sure."
The proud mum's post has since gone viral, shared over 70,000 times - and counting.
"I got the upgrade too," one commenter wrote. "What fun we have. Yes would definitely recommend the upgrade!"
"That extra chromosome truly carries more love for the world!!" said another. "They are simply amazing packages and the best. Just like every other package but offer way more to the world and they are honestly the most loving children you will ever meet."
The Mighty, Ms Egan said that reading posts from parents of children with Down syndrome helped her when she was expecting her baby girl - and she wanted to do the same. "That is the reason I wanted to share my experience, and doing it as a product review struck me as a lighthearted and accessible way to do so."
At the time she received the diagnosis, Ms Egan explained that some of her co-workers were also expecting and experiencing "textbook pregnancies."
"All I could think when I received the diagnosis was that my baby wouldn't be as accepted and celebrated as everyone else's had been," she added.
Originally devastated, Ms Egan said she and her husband grieved before deciding to connect with their local Down syndrome association. Meeting other families made them feel "hopeful" again and excited to meet their little girl.
Ms Egan's post comes ahead of World Down Syndrome Day on 21 March, with this year's theme: "no one left behind'. In the lead up, Down syndrome Australia will be sharing 21 stories from people with Down syndrome in response to the question: "What makes me proud."