ABSTRACT
Rupture of membranes at term, whether spontaneous or artificial, causes rapid and sustained increase in prostaglandin F2α (PGF2α ) metabolite (PGFM) levels and is associated with augmentation of uterine contractions. To investigate why premature rupture of membranes (PROM) often fails to initiate uterine contractions, we measured plasma concentrations of PGFM and oxytocin (OT) in patients with PROM near term. Serial blood samples were taken before and after PROM as well as before and after local PGE2 gel application for cervical ripening. For comparison, patients with similar criteria with intact membranes were also studied, as were patients in spontaneous labor at term with and without spontaneous rupture of membranes. PROM was always associated with an initial, marked increase in plasma PGFM. Whether or not this increased PGF2α production was maintained was related to the cervical status at the time of PROM. In patients with unripe cervix PGFM levels returned to initial levels within 2 hours and no contractions were elicited; when the cervix was 3 cm or more dilated, PGFM levels remained high and contractions began within 1 to 3 hours. PROM had no significant effect on plasma OT levels. When PGE2 gel was applied to ripen the cervix, PGFM levels increased moderately within 30 minutes in all patients regardless of the status of the membranes. In patients with intact membranes the concentration of PGFM in plasma declined to initial levels within 4 hours, whereas in patients with PROM, PGFM levels remained increased throughout the study period. PGE2 application increased plasma OT levels in patients with unripe cervix (less than 2 cm) but not in those with cervix more than 3 cm dilated. We conclude that the ability of uterine tissues to sustain increased PGF2α , production in vivo after rupture of membranes depends on the degree of cervical ripeness. Increases in PGF2α production in 1- to 2-hour duration are not sufficient to initiate labor in patients with an unripe cervix.
