The accumulation of prostaglandins (PG) in amniotic fluid is an aftereffect of labor and not indicative of a role for PGE2 or PGF2 alpha in the initiation of human parturition.

The accumulation of prostaglandins (PGs) in amniotic fluid (AF) during labor is cited frequently as one line of evidence in support of a role for these eicosanoids in the initiation of human parturition. In this study, we evaluated an alternate possibility, viz. that PGs entering AF at parturition are produced as a sequela of labor-associated processes. During labor, the AF normally becomes separated into two compartments, viz. the forebag and the upper compartment, by the obstruction produced as the descending fetal presenting part is engaged in the maternal pelvis. We theorized that the PGs that enter AF are produced in traumatized tissues lining the forebag, which is formed as the result of labor-driven cervical dilatation. In addition, these traumatized tissues are exposed to and bathed by the vaginal fluid, which contains many potent stimuli of PG formation, viz. large numbers of microorganisms and bacterial toxins. AF was collected at term before labor (n = 50) and from the upper compartment during labor (n = 47) by transuterine amniocentesis, and AF was collected by direct needle aspiration of the forebag during labor (n = 143). PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and PGE2 were quantified by RIA. The concentrations (nanomoles per L mean +/- SEM) of PGs in AF of the forebag (PGF2 alpha, 85.6 +/- 10.6; PGFM, 20.8 +/- 2.58; PGE2, 26.9 +/- 2.73) were much greater than those in the AF before labor (PGF2 alpha, 0.56 +/- 0.05; PGFM, 0.9 +/- 0.08; PGE2, 5.89 +/- 1.13) or in AF of the upper compartment during labor (PGF2 alpha, 7.14 +/- 1.64; PGFM, 5.11 +/- 0.82; PGE2, 8.74 +/- 1.71). The concentrations of PGs in AF of the upper compartment during early labor (< or = 2.5-cm cervical dilatation) were no greater than those in AF before labor began. The concentration and total content of PGs in AF of the forebag increased as a function of cervical dilatation until delivery. At 3- to 5-cm cervical dilatation, the levels of PGs in AF of the upper compartment were greater than those before labor, but significantly less than those in AF of the forebag at the same stage of labor progress. After 3-5 cm, the levels of PGs in the upper compartment did not increase further. These findings indicate that PGF2 alpha, PGFM, and PGE2, which enter AF in increased amounts during parturition, are produced during, not before, labor in tissues (principally decidua) lining for forebag.(ABSTRACT TRUNCATED AT 250 WORDS)