The second series of the show will consist of eight episodes, compared with the six-part first series.
There are high hopes for the new series, with the majority of the first episode taking place on a boat at sea.
It will feature Trixie (Helen George) and Sister Evangelina (Pam Ferris) caught in strange circumstances aboard a Swedish cargo-ship.
While out at sea, the action sees them helping the Captain's daughter, who is expecting her first child.
In one scene, Trixie and Sister Evangelina end up scaling the outside of the ship on a rope ladder.
The news series comes after the first drew in an average of 8.7 million viewers across the six episodes.
Then the recent Christmas special, in which a baby was abandoned on the steps of Nonnatus House, was the third most watched show on Christmas Day, with an audience of 10.1m tuning in.
The programme will be available on BBC iPlayer
, where there is also a gallery of images and clips to view before it airs.