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1. Definition The third stage of labour starts immediately after the delivery of the infant and ends with the delivery of the placenta and membranes .

2. Duration Normally 5 – 15 minutes. 30 minutes have been suggested if there is no evidence of significant bleeding.

3. Causes of Placental Seperation Aefter delivery of the fetus the uterus retracts and the placental bed diminished. As the placenta is inelastic and does not diminish in size it seperates .

4. Physiological Changes During 3 rd Stage of Labour Placenta seperation Expulsion of placenta Control of bleeding

5. Placenta S eperation The process of placenta seperation duing and after birth are as follows: The surface area of the uterine cavity gradually increases during pregnancy and rapidly decreases during the second stage of labor . The surface area of the uterine cavity gradually increases during pregnancy and rapidly decreases during the second stage of labor .

6. Cont.. The placenta is separated from the decidual attachment by the action of the uterine muscle . As the baby gradually leaves the uterus, the cavity of the uterus must become progressively smaller to permit the uterine wall to remain closely approximated to the baby. This maintains the expulsive force of the muscular contractions on the body of the baby.

7. Cont.. The mechanism for achieving this close approximation is through a slight shortening or retraction of the individual muscle fibers during each contraction. Slow delivery of the shoulders and body of the infant will permit the muscle fibers to retract and adjust to the reduction in size of the cavity, thereby promoting more efficient contractions. As the surface area of the interior of the uterus slightly reduces the diameters of the placental site, the placenta becomes thicker and decreases slightly in diameter.

8. Cont.. Since the placenta has a limited ability to alter its surface area, it must separate if the area to which it is attached is reduced considerably in size. The separation, which occurs in the outer portion of the spongy layer of the decidua basalis , begins during the later second stage of labor and is usually completed as the uterus contracts during the final expulsion of the baby . The effectiveness of this process depends on the extent to which the placental site is reduced. If the contractions are firm and forceful, the placenta may be expelled almost immediately after the baby is born. However, if they are less effective, complete placental separation may be delayed.

9. Cont.. The blood sinuses at the placental site, which have been opened by partial or complete separation of the placenta, are the source of bleeding during and after the third stage of normal labor. This bleeding is controlled initially by firm contraction of the interlacing uterine muscle bundles around the branches of the uterine arteries . the vessels are compressed and kinked bleeding from the open ends is slight if the uterine muscle is relaxed, the bleeding will be brisk and continuous.

10. T he process of expulsion of the placenta after separation Expulsion of the placenta is a function of abdominal, uterine, and gravitational forces and cord traction by the attendant . After separation, blood accumulates behind the placenta, and the uterus rises in the abdomen. A firm uterine contraction now begins, and the uterus changes from a flattened, soft, discoid organ to one that is firm and globular. This process can take from several minutes to much longer, depending on the strength of the uterine contractions and the location of the placenta within the uterus. A lower implantation will mean less firm contractions in the lower uterine segment and a longer time for separation and expulsion.

11. Cont.. During a uterine contraction, the flattened uterine body of the uterus becomes globular as the placenta is forced downward into the lower uterine segment .