Sami wrote: "Baaaaaaaabes!!!!! Wahhhhhh can't wait to meet her!!!"
The Māori actress who rose to fame as a young girl when she starred in Whale Rider shared a photo of her baby bump in February.
"Thank you to my sisterhood for celebrating our pēpī. We feel so deeply loved."
In a statement to the Herald in February, Castle-Hughes said she and her husband were "thrilled" to be expecting their first child together.
In May, Castle-Hughes opened up about the reality of juggling work and motherhood when she celebrated the season two wrap of her show FBI: Most Wanted.
"I am so grateful for you all. Especially for loving this Mama & always making space (sometimes literally) for me & my bump.
"To all the Mamas just doing the thing because we gotta, the respect is beyond. I see you and I celebrate you!"
In January, the star married Grahamer in New York. She shared beautiful photos of the couple together, with Castle-Hughes donning a floor-length floral dress.
The 30-year-old star has one child she shares with her ex-boyfriend Bradley Hull, a daughter named Felicity who was born in 2007. Castle-Hughes was 17 at the time.
She was previously married to Jonathan Morrison, but they divorced in 2016 after marrying on Valentine's Day in 2013.
Castle-Hughes was nominated for an Academy Award for her role as Paikea in Whale Rider, an incredible feat for the then 13-year-old who had no prior acting experience. She was just 11 when she starred in the movie.
