"We all have to deal with various struggles and challenges in life. And sometimes it's easier to only showcase the good times on social media, which is what leads many people to criticize it for its lack of authenticity," she then wrote.
"Having so many people follow me on Instagram and read my posts is both incredibly humbling and hugely uplifting," the actress continued. "The support and affection that so many of you show me lifts me up during even my darkest days, one of which happened last year after I miscarried and lost the child of my hopes and dreams."
Mitchell, 31, also shared a photo of a sonogram with a broken heart emoji over it.
"In the spirt of the new year, I think that we need to remember that we are all on this journey together -- in good times and in bad -- and to remind ourselves that we seldom really know or understand the struggles and hardships that other people are going through," she continued.
Then, her plea for the new year: "So, for 2019, let's all try to be a little more compassionate, empathetic, patient and thoughtful with each other." She added, "This sounds like a great resolution to me. I hope that you agree. Happy New Year everyone."