Conditions of the cervix for the increase of plasma levels of 13,14-dihydro-15-keto-prostaglandin F2 alpha after amniotomy at term.

Amniotomy was performed in 12 multiparas at term but not in labor. In 6 of these patients (group I), the fetal head and cervix condition were favorable for amniotomy, and in the other 6 (group II), they were not favorable. In all group I patients, a sudden and progressive descent of the fetal head, and onset and progress of labor were noted within 5 hours. Plasma 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) levels increased significantly (P less than 0.05) in 4 of these cases with time. In group II patients, descent of the head was less than that in group I patients (P less than 0.05), and neither strong labor nor rise of PGFM levels was noted within 5 hours. These data support our view that amniotomy at an appropriate time results in the onset and progress of labor, and the rise of plasma PGFM in virtue of the sudden and exponential increase of the head to cervix force, but amniotomy at an inappropriate time does not, because this force is unchanged.