Plasma Prostaglandin E2 Metabolite Levels During Labor Induction With a Sustained-Release Prostaglandin E2 Vaginal Insert

Objective: To measure prostaglandin E₂ levels during labor induction with a sustained-release vaginal polymer insert (prostaglandin E₂ insert) and to determine whether Bishop score change correlated with tachysystole.

Methods: Twelve primiparas and 12 multiparas were treated with a 0.3 mg per hour sustained-release polymer vaginal prostaglandin E₂ insert for up to 24 hours. Bishop score was assessed at start and end of therapy, and serum samples were collected at 4-hour intervals. Prostaglandin E₂ metabolite (PGEM) levels were measured by specific enzyme immunoassay.

Results: Exposure averaged 13.5 ± 7.2 hours. Four patients (16.7%, three nulliparas) had tachysystole. Mean PGEM levels increased from 187 ± 42 pg/mL at baseline to 548 ± 110 pg/mL at 12 hours (P < .05) and remained relatively stable thereafter. Nulliparas with Bishop score changes of four points or more had the highest increase, with average peak levels of 985 ± 109 pg/mL, compared with 452 ± 58 pg/mL for all others (P < .001). Patients with tachysystole had higher 4-hour (P < .01) and overall (P < .04) increases in PGEM level. Removal of the insert led to an average decrease of 335 pg/mL in PGEM levels (P < .01). The decrease correlated with the PGEM level measured before removal (r = .94, P < .0001) and the maximum PGEM increase from baseline (r = .94, P < .0001). The mean mixed venous cord PGEM level was 409 ± 375 pg/mL.

Conclusion: Administration of the prostaglandin E₂ insert led to a sustained increase in circulating PGEM levels in women who had labor induction. Peak PGEM levels correlated with Bishop score improvement. Rapid increases in prostaglandin E₂ levels might cause tachysystole.