THE PERINATAL PERIOD, IS INCREASED IN THE AMNIOTIC FLUID OF WOMEN WITH PRETERM LABOR AND INTACT MEMBRANES LARA FRIEL, JIMMY ESPINOZA, SAMUEL EDWIN, JYH KAE NIEN, RICARDO GOMEZ, SONIA HASSAN, TINNAKORN CHAIWORAPONGSA, ROBERTO ROMERO, Wayne State University School of Medicine, Department of Obstetrics and Gynecology, Detroit, Michigan, Perinatology Research Branch, NICHD, NIH, DHHS, Detroit, Michigan, CEDIP, Sotero del Rio Hospital, OB-GYN, Universidad Catolica de Chile, Puento Alto, Chile OBJECTIVE: The multigenic S100 protein family has recently emerged as important intracellular and extracellular regulatory molecules, playing key roles in the regulation of inflammatory cells and neurons. An elevated concentration of S100b in neonatal plasma or urine is a risk factor for brain damage in the perinatal period. The present study was conducted to determine if S100b is detectable in amniotic fluid (AF), where the kinetic conditions may allow for detection of prior intrauterine insults. In addition, we studied S100b in patients with AF infection, since its production can be induced by proinflammatory cytokines. STUDY DESIGN: Amniotic fluid concentrations of S100b were measured in the following groups: 1) midtrimester (n=74); 2) term not in labor (n=27); 3) term in labor (n=51); 4) preterm labor who delivered at term (n=35); 5) preterm labor who delivered preterm (n=52); 6) preterm labor with intraamniotic infection, (IAI; n=25); 7) PPROM without IAI (n=26); and 8) PPROM with IAI (n=26); AF S100b concentration was measured by sensitive immunoassay. Kruskal Wallis ANOVA and post-hoc tests were used for analysis. RESULTS: 1) S100b was detected in all AF samples; 2) The AF concentration of S100b did not change with gestational age (midtrimester vs. term; p=0.76); 3) There was no significant difference in AF concentration of S100b between patients with labor at term vs. no labor (p=0.20); 4) Among patients with PTL, those with IAI had significantly higher S100b AF concentration [median: 1133.6 pg/ml (23.3-29,221)] than those who delivered preterm without IAI [median: 95.1 pg/ml (23.3-4732); p!0.05] or those who delivered at term [median: 51 pg/ml (23.3-130); p!0.05] and 5) In contrast, there was no significant difference in the AF S100b concentration between patients with PPROM with IAI and without IAI (p=0.066). CONCLUSION: 1) S100b is a physiologic constituent of AF; 2) AF concentrations are elevated in patients with IAI and an intensive inflammatory response; 3) An elevation in AF concentration of S100b may reflect inflammation rather than neurologic injury.