[Observation of course of placental separation by continuous dynamic ultrasonography during third stage of labor].

Objective: To investigate the physiologic course of third stage of labor, and to judge the optimal time of natural placental separation permitted.

Methods: To observe and record the course of third stage of labor by continuous dynamic ultrasonography and to estimate the total amount of blood loss from placental separation within two hours after delivery by the method of weighing lost blood.

Results: Third stage of labor can be divided into four phases: the latent phase (4.37 +/- 3.78) min, the contraction phase (1.48 +/- 0.97) min, the detachment phase (0.50 +/- 0.00) min, and the expulsion phase (0.62 +/- 2.23) min. In 85% of the puerperas the third stage of labor takes about 10 minutes (average 6.94 minutes). The amount of postpartum hemorrhage and the risk of the patient increased prominently if the time of stage of labor was longer than 10 minutes (P < 0.01).

Conclusion: The third stage of labor must be limited in 10 minutes to prevent postpartum hemorrhage.