Essential factors of labor(14) LABOR FORCE-- retraction
If contraction was followed by complete relaxation no progress would be made, in retraction some of the shortening of the fibres is maintained. So the uterine cavity becomes progressively smaller with each contraction.
The net effect of retraction in normal labor are:
-- essential property in the formation of lower segment and dilation and taking up of the cervix
-- to maintain the advancement of the presenting part made by the uterine contraction and to help in ultimate expulsion of the fetus
-- to reduce the surface area of the uterus favouring separation of placenta