Objective: The purpose of this study was to examine the relationship between rupture of membranes, labor, and microbial invasion of the amniotic cavity and amniotic fluid concentrations of eicosanoids in patients with spontaneous rupture of membranes at term.
Study design: Amniotic fluid was retrieved by transabdominal amniocentesis from patients with rupture of membranes and patients with intact membranes at term. Studies to determine the microbial state of the amniotic cavity included culture for bacteria and mycoplasmas, Gram stain, amniotic fluid white blood cell count, and Limulus amebocyte lysate. Eicosanoids (prostaglandin E2, prostaglandin F2 alpha and its stable metabolite, 6-keto-prostaglandin F1 alpha, and thromboxane B2) were determined with sensitive and specific radioimmunoassays validated for human amniotic fluid. Statistical inference was conducted with analysis of variance and linear contrast.
Results: (1) Spontaneous rupture of membranes at term was associated with a significant increase in amniotic fluid concentrations of all eicosanoids measured in this study except 6-keto-prostaglandin F1 alpha. (2) Early labor in patients with rupture of membranes was associated with a significant increase in the amniotic fluid concentration of all eicosanoids. (3) A significant increase in amniotic fluid eicosanoids in women with microbial invasion of the amniotic cavity could not be documented.
Conclusions: Whereas preterm labor in the absence of microbial invasion of the amniotic cavity is not associated with a significant increase in amniotic fluid concentrations of prostaglandins, a clear increase was documented in women with early labor after spontaneous rupture of membranes. These observations suggest that there are fundamental differences in the biochemistry of term and preterm parturition.