Casting is already underway for an actress to play West Indian nurse Lucille in the next series.
It's to reflect the influence of nurses from the Commonwealth on the NHS in the 1960s.
Series creator Heidi Thomas said Lucille will be "elegant, funny and clever" and bring "a fresh new energy to life at Nonnatus House".
"My research is continually bringing up new things," Thomas told the BFI & Radio Times Television Festival.
"[It] has made me very aware of the contributions made by West Indian and Caribbean nurses to the NHS in the early 1960s. She's going to bring stories with her, and a different cultural point of view, and that's very exciting."
Series six of the popular drama finished last month, concluding with a birth, death and a marriage in the final episode.
It will return to BBC One for a Christmas special, before series seven kicks off in the new year.
The casting news comes as Call the Midwife was voted the best TV drama of the 21st Century in a Radio Times poll.
It beat finalists The Night Manager, The West Wing, The Bridge, Happy Valley and Merlin, which won separate genre categories last week.
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