"Just got my beautiful ring. Ethical diamonds in rose gold band with a rose quartz crystal — stone of the heart. Exactly me, " the 27-year-old wrote.
Teresa, who is also pregnant with her first baby, has had to wait to wear her new band while it was resized. The excited star took to wearing a different ring on her engagement finger as a representative.
It's been quite a month for the Warm Bodies actress and her fiancé. One week after announcing their engagement, the couple revealed that they were expecting their first baby together.
Teresa posted a picture of a sonogram and a pair of knitted baby booties, with a caption that began, "This is where my heart is".
"To my precious baby — I'm so blessed to be your mama, we have been wishing for you awhile," she wrote. "We love you so much and can't wait to kiss your little face and tiny toes. Thank you for hearing our prayers."
Touched by her followers' well wishes, she later posted, "Thanks for all the beautiful messages! Those who know me best know that this is something I've been waiting for my whole life."
The sonogram shared by the star was taken on 8 August — five days after Teresa announced her engagement to American actor-director Mark, 33, who has a son, Isaac, from his previous relationship with actress Frankie Shaw.
"I think I've said the word 'fiancé' over 100 times in the last few hours," Teresa excitedly told her Twitter followers. "It sounds so nice. So happy."
Teresa and Mark live together in LA — five-year-old Isaac lives with them part time. They plan to split their time between Hollywood and Teresa's hometown of Adelaide, Australia.