DYNAMIC ULTRASONOGRAPHIC IMAGING OF THE 3RD STAGE OF LABOR - NEW PERSPECTIVES INTO 3RD-STAGE MECHANISMS

OBJECTIVE: Dynamic ultrasonographic imaging of the third stage of labo r was performed to document ultrasonographic findings and to present n ew perspectives into third-stage mechanisms. STUDY DESIGN: Twenty-five normal deliveries and five with prolonged third-stage labor were stud ied. RESULTS: Normal third-stage labor could be divided into four phas es: (1) latent phase, characterized by thick, placenta-free wall and t hin, placenta-site wall; (2) contraction phase, with thickening of pla centa-site wall (from < 1 cm to > 2 cm); (3) detachment phase, in whic h the placenta completes its separation and detaches; and (4) expulsio n phase, with a sliding movement of the placenta. Although oxytocic ag ents were routinely used, they do not seem to influence the findings. In five cases with retained placenta the placenta-site wall was initia lly thin. In four of them it became thick, and the placenta was remove d by traction of the cord, whereas in the fifth case the placenta-site wall remained thin and the placenta had to be removed manually. CONCL USION: Shearing forces seem to tear the decidual septae and thereby se parate the placenta. This process is completed only when the placenta- site wall attains full thickness. In cases of prolonged third-stage la bor, traction of the cord should be applied only when this phase is co mpleted and the actual sliding movement of the placenta is observed.