F prostaglandin levels in amniotic fluid during balloon-induced cervical softening and labor at term.

Mechanical stretching of the uterus was applied to seven term patients not in labor with unripe cervix by means of intra-uterine application of a rubber balloon. Significant cervical softening, and initiation and progress of labor was achieved in all cases. Serial analyses of the F prostaglandins (PGF) in amniotic fluid were performed before and at given intervals of cervical dilatation. Before the application of stretch, the levels of PGF varied greatly: the values in 5 cases were measureable but low (less than 645 pg/ml) and in two cases the levels were below the sensitivity of the assay (less than 50 pg/ml). Large fluctuations of the levels were noted in many cases during the treatment. However, the rise of the PGF values was significant with the progress of cervical dilatation compared to the pre-treatment values (P less than 0.05 at both 3-4 and 5-6 cm, and P less than 0.01 at 9-10 cm). It was concluded that the increased release of PGF in amniotic fluid is mediated by uterine stretching, and that upon being released PGF is probably involved in the cervical softening an progress of labor.