The 1950s-set drama will return to BBC One on Sunday, January 20 at 8pm, the channel has confirmed.
The highly successful and popular series will run for an extended eight episodes.
Call the Midwife became a record-breaking ratings success for the BBC in early 2012.
Based on the best-selling memoirs of Jennifer Worth, the drama follows newly qualified midwife Jenny Lee (Jessica Raine) and the work of her colleagues and the nuns of Nonnatus House, a nursing convent.
Jenny Agutter, Pam Ferris, Miranda Hart, Judy Parfitt and Laura Main are also among the cast.
Miranda Hart has been nominated for 'Best Female Drama Performance' for her role as Camilla 'Chummy' Fortescue-Cholmondeley-Browne.
A soundtrack album has been announced for a release in time for Mother's Day.