Amniotic fluid glucose concentration: a rapid and simple method for the detection of intraamniotic infection in preterm labor.

The purpose of this study was to determine whether amniotic fluid glucose concentrations is of value in the rapid diagnosis of intraamniotic infection. Amniocenteses were performed in 168 patients with preterm labor and intact membranes. Amniotic fluid was cultured for aerobic and anaerobic bacteria, as well as Mycoplasma species. The prevalence of positive amniotic fluid cultures was 13.6% (23/168). Patients with positive amniotic fluid cultures for microorganisms had significantly lower median amniotic fluid glucose concentrations than patients with negative amniotic fluid cultures (median 11 mg/dl, range 2 to 30 mg/dl vs median 28 mg/dl, range 3 to 74, respectively; p less than 0.001). Amniotic fluid glucose concentrations below 14 mg/dl had a sensitivity of 86.9% (20/23), a specificity of 91.7% (133/145), a positive predictive value of 62.5% (20/32), and a negative predictive value of 97.8% (133/136) in the detection of a positive amniotic fluid culture. Amniotic fluid glucose determination is a rapid, sensitive, inexpensive, and simple test for the detection of intraamniotic infection in women with preterm labor and intact membranes.     

Amniotic fluid glucose and intraamniotic infection

Thirty-nine patients with either premature labor and/or preterm premature ruptured membranes underwent transabdominal amniocentesis to enable the following amniotic fluid analyses to be performed: culture and sensitivity, Gram's stain, and glucose determination. All nine patients with intraamniotic infection had amniotic fluid glucose values less than 10 mg/dl. Three patients with amniotic fluid glucose levels less than 10 mg/dl but without chorioamnionitis were delivered of infants within 72 hours of admission. The mean amniotic fluid glucose level of patients with intraamniotic infection (5 +/- 2.4 mg/dl) was significantly lower than in those without intraamniotic infection (39.8 +/- 18.42 mg/dl). All patients with amniotic fluid glucose values less than 10 mg/dl had either bacteria and/or white blood cells on Gram's stain. Two patients without chorioamnionitis had white cells on Gram's stain and amniotic fluid glucose values greater than 10 mg/dl. It appears that amniotic fluid glucose is more sensitive and more specific than Gram's stain in the diagnosis of intraamniotic infection. All 12 patients with low amniotic fluid glucose values were delivered of infants within 72 hours as the result of either the presence of infection or the progression of labor.     

Dual roles of amniotic fluid nitric oxide and prostaglandin E2 in preterm labor with intra-amniotic infection.

We hypothesized that induction of nitric oxide synthase and cyclo-oxygenase-2 by bacterial products in intra-amniotic infection could increase the production of proinflammatory nitric oxide and prostaglandin E2 (PGE2) and cause preterm labor. Thus, we sought to determine amniotic fluid levels of nitric oxide metabolites (NOx) and PGE2 in preterm labor patients with and without intra-amniotic infection. Amniotic fluid from 13 preterm labor patients with intra-amniotic infection and 24 without intra-amniotic infection were studied. Intra-amniotic infection was defined as the presence of a positive amniotic fluid culture. Amniotic fluid was tested for NOx, PGE2, glucose, leukocyte counts, Gram stains, creatinine, pH, and specific gravity. NOx was determined using Griess reagent after reduction of nitrate to nitrite with aspergillus nitrate reductase. PGE2 was measured by an enzyme-linked immunoassay. Both amniotic fluid NOx and PGE2 were normalized by amniotic fluid creatinine. We found that amniotic fluid concentrations of NOx and PGE2 were significantly higher in preterm labor patients with intra-amniotic infection compared to those without intraamniotic infection (NOx: median 1.8 micromol/mg creatinine, range 0.7 to 6.8 vs. 1.3 micromol/mg creatinine, range 0.9 to 2.1, p=0.03; PGE2: median 33.5 ng/mg creatinine, range 0.0 to 1048.6 vs. 0.0 ng/mg creatinine, range 0.0 to 33.6, p=0.004). In addition, amniotic fluid NOx and PGE2 were positively correlated (r=0.343, p=0.0398). We conclude that there may be an interaction between the nitric oxide and prostaglandin pathways in intraamniotic infection. Increased production of amniotic fluid pro-inflammatory nitric oxide and PGE2 may play an important role in the pathogenesis of preterm labor in patients with intra-amniotic infection.     

Tumor necrosis factor in preterm and term labor.

OBJECTIVE: Our objective was to determine if labor (term and preterm) and microbial invasion of the amniotic cavity were associated with changes in amniotic fluid concentrations of tumor necrosis factor. STUDY DESIGN: Amniotic fluid was retrieved by transabdominal amniocentesis from 269 women in the following groups: midtrimester (n = 38), preterm labor with intact membranes (n = 52), preterm premature rupture of membranes (n = 74), term in active labor (n = 84), and term not in labor (n = 21). Fluid was cultured for aerobic and anaerobic bacteria and for Mycoplasma species. Tumor necrosis factor was measured with a commercially available enzyme-linked immunosorbent assay validated for amniotic fluid (sensitivity 60 pg/ml). RESULTS: Amniotic fluid from pregnant women in the second and third trimesters who were not in labor did not contain tumor necrosis factor. Among women in preterm labor, 92.3% (12/13) of patients with a positive amniotic fluid culture had detectable tumor necrosis factor in the amniotic fluid (median 820 pg/ml, range less than 60 to 2340 pg/ml). In contrast, only 10.2% (4/39) of women with a negative amniotic fluid culture had detectable tumor necrosis factor. Histopathologic chorioamnionitis was found in all patients who had a positive amniotic fluid culture, and tumor necrosis factor was detectable in the amniotic fluid of all but one of these patients. Among women in active labor at term, 25% (21/84) had detectable tumor necrosis factor in the amniotic fluid. Tumor necrosis factor was detected more frequently in the amniotic fluid of patients with a positive amniotic fluid culture than in patients with a negative culture (46.6% [7/15] vs 20.2% [14/69], p = 0.047). Amniotic fluid concentrations of tumor necrosis factor were significantly higher in patients with preterm premature rupture of membranes, labor, and a positive amniotic fluid culture than in the other subgroups of patients with preterm premature rupture of membranes. CONCLUSION: Parturition in the setting of microbial invasion of the amniotic cavity is associated with activation of the cytokine network as demonstrated by the detection of tumor necrosis factor in human amniotic fluid.     

Clinical significance of intra-amniotic inflammation in patients with preterm labor and intact membranes.

OBJECTIVE: The purpose of this study was to determine the frequency and clinical significance of intraamniotic inflammation in patients with preterm labor and intact membranes. STUDY DESIGN: Amniocentesis was performed in 206 patients with preterm labor and intact membranes. Amniotic fluid was cultured for aerobic and anaerobic bacteria and mycoplasmas. The diagnosis of intraamniotic inflammation was made in patients with a negative amniotic fluid culture on the basis of amniotic fluid concentrations of interleukin-6 (>2.6 ng/mL, derived from receiver operating characteristic curve analysis). Statistical analysis was conducted with contingency tables and survival techniques. RESULTS: Intra-amniotic inflammation (negative amniotic fluid culture but elevated amniotic fluid interleukin-6) was more common than intra-amniotic infection (positive amniotic fluid culture regardless of amniotic fluid interleukin-6 concentration; 21% [44/206 women] vs 10% [21/206 women]; P <.001). The amniocentesisto-delivery interval was significantly shorter in patients with intra-amniotic inflammation than in patients with a negative culture and without an inflammation (median, 20 hours [range, 0.1-2328 hours] vs median, 701 hours [range, 0.1-3252 hours], respectively; P <.0001). Spontaneous preterm delivery of <37 weeks was more frequent in patients with intra-amniotic inflammation than in those with a negative culture and without inflammation (98% vs 35%; P <.001). Patients with intra-amniotic inflammation had a significantly higher rate of adverse outcome than patients with a negative culture and without intra-amniotic inflammation. Adverse outcomes included clinical and histologic chorioamnionitis, funisitis, early preterm birth, and significant neonatal morbidity. There were no significant differences in the rate of adverse outcomes between patients with a negative culture but with intra-amniotic inflammation and patients with intra-amniotic infection (positive culture regardless of amniotic fluid interleukin-6 concentration). CONCLUSION: Intra-amniotic inflammation/infection complicates one third of the patients with preterm labor (32%; 65/206 women), and its presence is a risk factor for adverse outcome. The outcome of patients with microbiologically proven intra-amniotic infection is similar to that of patients with intra-amniotic inflammation and a negative amniotic fluid culture. We propose that the treatment of patients in preterm labor be based on the operational diagnosis of intra-amniotic inflammation rather than the diagnosis of intra-amniotic infection because the latter diagnosis cannot be undertaken rapidly.     

Intraamniotic infection and the onset of labor in preterm premature rupture of the membranes

The purpose of this study was to examine the relationship between intraamniotic infection and the onset of labor in patients with preterm premature rupture of the membranes. Two hundred and thirty consecutive patients were admitted with premature rupture of the membranes to Yale-New Haven Hospital from January 1985 to July 1987. Amniotic fluid was retrieved by amniocentesis from 96% (221/230). Sixty-one patients were in labor on admission (27.6%, 61/221) and 39% of them (24/61) had a positive amniotic fluid culture. Patients in labor on admission were more likely to have a positive amniotic fluid culture than those who were not in labor on admission (24/61 versus 41/160, p = 0.049). Of the 160-patients who were not in labor on admission, 81 subsequently went into spontaneous labor; microbiologic information at the time of labor was known in 48 of these patients (59.2%). Seventy-five percent (36/48) of these patients had a positive amniotic fluid culture. The incidence of intraamniotic infection in quiescent women who subsequently went into labor was higher than that of patients admitted in active labor (75% versus 39%, p = 0.0004). These results provide a basis for the clinical impression that the onset of labor in women with preterm premature rupture of the membranes is associated with a subclinical intraamniotic infection. The mechanisms responsible for the onset of labor in women without an intraamniotic infection may be associated with an extraamniotic infection (e.g., deciduitis) or a noninfectious process.     

A role for the novel cytokine RANTES in pregnancy and parturition.

OBJECTIVE: RANTES (regulated on activation, normal T cell expressed and secreted), a potent and versatile chemokine, is capable of attracting monocytes, lymphocytes, basophils, and eosinophils. This cytokine has been implicated in the regulation of the inflammatory response and in the recruitment of macrophages to the implantation site in early pregnancy. RANTES messenger ribonucleic acid and protein have been detected in fetal tissue and first-trimester trophoblast in response to bacterial endotoxin. The purpose of this study was to determine whether intrauterine infection, parturition (preterm and term), and gestational age affect the amniotic fluid concentrations of RANTES in human pregnancy. STUDY DESIGN: A cross-sectional study was designed to examine the relationship between labor, microbial invasion of the amniotic cavity, gestational age, and RANTES expression in amniotic fluid. Amniotic fluid was obtained from 214 women in the following groups: (1) midtrimester (n = 22), (2) preterm labor with intact membranes in the presence (n = 20) or absence (n = 74) of microbial invasion of the amniotic cavity, (3) term, not in labor (n = 44) and term, in labor in the presence (n = 27) and absence (n = 27) of microbial invasion of the amniotic cavity. Microbial invasion of the amniotic cavity was defined as a positive amniotic fluid culture for microorganisms. RANTES concentrations were determined by use of a sensitive and specific immunoassay. RESULTS: (1) Amniotic fluid RANTES concentrations decrease with advancing gestational age (r = 0. 43; P <.01). (2) Labor at term was associated with an increase in median concentrations of RANTES (labor-median, 8.4 pg/mL; range, <1.3-94.4 vs no labor-median, <1.3 pg/mL; range, <1.3-230.3; P <.01). (3) Women with preterm labor who delivered preterm (no microbial invasion of the amniotic cavity) had a higher median concentration of amniotic fluid RANTES than those who delivered at term (median, 12.7 pg/mL; range, <1.3-928 vs median, <1.3 pg/mL; range, <1.3-127. 5; P <.001). (4) Microbial invasion of the amniotic cavity was associated with a significant increase in median amniotic fluid RANTES in both preterm and term labor (preterm labor with microbial invasion of the amniotic cavity-median, 51.6 pg/mL; range, <1.3-2290 vs preterm labor without microbial invasion of the amniotic cavity-median, 12.7 pg/mL; range, <1.3-928 and vs preterm labor with delivery at term-median, <1.3 pg/mL; range, <1.3-127.5; P <.001 for each; term labor with microbial invasion of the amniotic cavity-median, 16.8 pg/mL; range, <1.3-171.4 vs term labor without microbial invasion of the amniotic cavity-median, 8.4 pg/mL; range, <1.3-94.4; P <.05 and vs no labor and no microbial invasion of the amniotic cavity-median, 1.4 pg/mL; range, <1.3-230.3; P <.001 and P <.05, respectively). CONCLUSION: These results support a role for RANTES in the mechanisms of human parturition and in the regulation of the host response to intrauterine infection.     

Evidence of participation of soluble CD14 in the host response to microbial invasion of the amniotic cavity and intra-amniotic inflammation in term and preterm gestations

Objective: Endotoxin has been implicated in the mechanism responsible for the setting of infection in preterm labor. To exert its biological effects, endotoxin binds to a circulating protein known as lipopolysaccharide binding protein (LBP) and presents endotoxin monomers to CD14, which may be a membrane-bound receptor or a soluble molecule. The endotoxin- LBP-CD14 complex interacts with Toll-like receptor 4 and other regulatory proteins leading to cellular activation and an inflammatory response. The purpose of this study was to determine whether microbial invasion of the amniotic cavity (MIAC)/intra-amniotic inflammation (both preterm and term) and parturition at term are associated with changes in the amniotic fluid and umbilical plasma soluble concentrations of CD14 (sCD14). Study design: Amniotic fluid was retrieved by amniocentesis from 88 patients in the following groups: group 1, preterm labor with intact membranes with MIAC/intra-amniotic inflammation (n = 18) and without these conditions (n = 26); group 2, term gestations not in labor without MIAC/intra-amniotic inflammation (n = 11), in labor without MIAC/intra-amniotic inflammation (n = 12) and in labor with MIAC/intra-amniotic inflammation (n = 13); and group 3, patients who underwent genetic amniocentesis at mid-trimester (n = 8). A sample of cord blood was obtained after delivery in all patients except those in group 3. sCD14 was assayed with a sensitive and specific immunoassay. Non-parametric statistics were used for analysis. A p value of < 0.05 was considered significant. Results: sCD14 was detectable in 97% (85/88) of the amniotic fluid samples. Amniotic fluid sCD14 concentrations were lower in patients at term than in the mid-trimester of pregnancy (mid-trimester: median 482 ng/ml, range 258-838 ng/ml vs. term no labor: median 7 ng/ml, range 2-274 ng/ml, p = 0.01). Among patients with preterm labor with intact membranes, the median amniotic fluid sCD14 level of patients with MIAC/intra-amniotic inflammation was higher than in patients without these conditions (median 1568 ng/ml, range 98-5887 ng/ml vs. median 645 ng/ml, range 0-3961 ng/ml, respectively; p = 0.01). Among women at term in labor, those with MIAC/intra-amniotic inflammation had a higher median amniotic fluid sCD14 concentration than those without these conditions (median 85 ng/ml, range 2-1113 ng/ml vs. median 17 ng/ml, range 0-186 ng/ml; p = 0.01). MIAC/ intra-amniotic inflammation in women with preterm labor with intact membranes was associated with a higher median umbilical venous plasma sCD14 concentration (median 744 ng/ml, range 0-3620 ng/ml vs. median 0 ng/ml, range 0-2060 ng/ml; p = 0.04). sCD14 was undetectable in plasma from umbilical cords of all neonates born to women at term. An increase in amniotic fluid concentration of sCD14 was observed in cases of intrauterine infection, not only by Gram-negative bacteria, but also Gram-positive bacteria and Ureaplasma spp. Conclusion: sCD14 is a physiological constituent of amniotic fluid, and its concentrations at term are lower than in the mid-trimester. Intrauterine infection/inflammation is associated with a higher median amniotic fluid sCD14 concentration in both preterm and term parturition. Neonates born from mothers with preterm labor with intact membranes and MIAC/intra-amniotic inflammation had a higher median concentration of sCD14 in umbilical cord plasma than those without these conditions. sCD14 concentrations are increased in the amniotic fluid and umbilical cord blood even in the absence of a microbiologically proven Gram-negative infection. CD14 appears to participate in the host response to intrauterine infection even in cases involving genital mycoplasmas.     

Amniotic fluid Interleukin-8 as a marker for intraamniotic infection

Summary We measured the amniotic fluid Interleukin-8 (AF IL-8) levels of 80 women to see whether or not AF IL-8 levels were of value in the diagnosis of intraamniotic infection. Of twelve patients developing conventional signs of infection, 9 had an AF IL-8 concentration above 10.000 pg/ml serum. In two patients, whose baby had a serious neonatal infection, AF IL-8 concentration also exceeded 10.000 pg/ml. Only one out of 66 apparently uninfected patients had an AF IL-8 level above 10.000 pg/ml. We therefore suggest that measuring the AF IL-8 levels is of value in cases of suspected intraamniotic infection.     

Evaluation of rapid diagnostic tests in the detection of microbial invasion of the amniotic cavity.

OBJECTIVE: We sought to determine and compare the value of several rapid diagnostic tests in the detection of intraamniotic infection. STUDY DESIGN: Gram stain, intraamniotic glucose level determination, leukocyte esterase assay, and the Limulus amebocyte lysate assay were performed on 144 amniotic fluid specimens retrieved by transabdominal amniocentesis in 136 patients with preterm premature rupture of the membranes or preterm labor. Diagnostic indices for a positive amniotic fluid culture and the development of clinical infection were calculated for each rapid test. Receiver-operator characteristic curves were generated to help select the optimal glucose level and combination of tests to detect intraamniotic infection. RESULTS: The greatest sensitivity for predicting either a positive culture or subsequent clinical infection in preterm labor patients and in predicting clinical infection in patients with preterm premature rupture of the membranes was demonstrated by a low glucose level. The Gram stain provided the greatest positive predictive value in patients with preterm labor. Combining the Gram stain and measurement of intraamniotic glucose levels did not improve sensitivity above glucose alone or positive predictive value above Gram stain alone. CONCLUSION: Leukocyte esterase determination and Limulus amebocyte lysate assay are insensitive indicators of intraamniotic infection. Selection of Gram stain or glucose level measurement alone or in combination as an appropriate screen for intraamniotic infection will depend on the clinicians' false-positive rate threshold.     

A study of the relationship between placenta growth factor and gestational age, parturition, rupture of membranes, and intrauterine infection

OBJECTIVE: Placenta growth factor is a potent angiogenic factor produced by the human placenta that has been implicated in the pathogenesis of preeclampsia and intrauterine growth restriction. Placenta growth factor belongs to the vascular endothelial growth factor family and is capable of inducing proliferation, migration, and activation of endothelial cells. The objective of this study was to determine the relationship between amniotic fluid concentration of placenta growth factor and gestational age, parturition (term and preterm), spontaneous rupture of the membranes, and intra-amniotic infection. STUDY DESIGN: Amniotic fluid samples obtained from 273 pregnant patients were assayed in the following clinical groups: midtrimester pregnancy, preterm labor who delivered at term, preterm labor without microbial invasion of the amniotic cavity who delivered preterm, preterm labor with microbial invasion of the amniotic cavity, term not in labor, term in labor, term with microbial invasion of the amniotic cavity, preterm premature rupture of membranes with and without microbial invasion of the amniotic cavity, and term with premature rupture of membranes without microbial invasion of the amniotic cavity. The placenta growth factor concentrations were determined by an immunoassay that is both sensitive and specific. RESULTS: Placenta growth factor was detectable in 96.3% (263/273) of samples. Amniotic fluid placenta growth factor concentration decreased with advancing gestational age (r = -0.42; P <.001). Amniotic fluid placenta growth factor concentrations were significantly higher in women in midtrimester pregnancy than in those at term not in labor (midtrimester pregnancy: median, 43.1 pg/mL; range, 22.9-69.8 pg/mL; vs term not in labor: median, 28.7 pg/mL; range, 16.1-82.7 pg/mL; P <.01). Neither term nor preterm parturition was associated with a change in amniotic fluid placenta growth factor concentrations. Term premature rupture of membranes was associated with a significant decrease in amniotic fluid placenta growth factor concentration (term premature rupture of membranes: median, 16.5 pg/mL; range <5.2-195.1 pg/mL; vs term intact membranes: median, 28.7 pg/mL; range, 16.1-822.7 pg/mL; P <.005). Preterm premature rupture of membranes was not associated with changes in amniotic fluid placenta growth factor concentrations. Intra-amniotic infection in preterm labor, term labor with intact membranes, and preterm premature rupture of membranes were not associated with changes in amniotic fluid placenta growth factor concentrations. CONCLUSION: Placenta growth factor is a physiologic constituent of amniotic fluid. Amniotic fluid concentrations of placenta growth factor decrease with advancing gestational age. Neither parturition nor infection affects amniotic fluid placenta growth factor concentrations.     

Infection and labor. V. Prevalence, microbiology, and clinical significance of intraamniotic infection in women with preterm labor and intact membranes

Amniotic fluid was retrieved by amniocentesis from 264 patients with preterm labor and intact membranes admitted to Yale-New Haven Hospital from Jan. 1, 1985, to July 31, 1988. The prevalence of a positive amniotic fluid culture was 9.1% (24/264). A total of 111 patients (42%) delivered preterm neonates, and 24 (21.6%) of those had positive amniotic fluid cultures. The diagnostic indexes of the Gram stain of amniotic fluid in the prediction of a positive amniotic fluid culture were as follows: sensitivity, 79.1%; specificity, 99.6%; positive predictive value, 95%; and negative predictive value, 98%. Endotoxin was detected with the limulus amebocyte lysate assay in 4.9% (13/264) of patients with preterm labor. All patients with endotoxin in the amniotic fluid delivered preterm neonates. The three most frequently isolated organisms were Ureaplasma urealyticum (n = 6), Fusobacterium species (n = 5), and Mycoplasma hominis (n = 4). Clinical chorioamnionitis was present in only 12.5% of the patients with positive amniotic fluid cultures. Women with positive amniotic fluid cultures had lower gestational ages and more advanced cervical dilatation on admission than women with negative cultures. Preterm infants born to mothers with positive amniotic fluid cultures had a higher incidence of respiratory distress syndrome and infectious complications than preterm neonates born after negative amniotic fluid cultures. These data underscore the frequency and importance of intraamniotic infections in women with preterm labor.     

C-reactive protein in vaginal fluid of patients with preterm premature rupture of membranes

OBJECTIVE: To assess whether C-reactive protein (CRP) concentrations in cervical amniotic fluid reflect the condition of the intrauterine environment in patients with preterm premature rupture of membranes (PROM) before 35 weeks of gestation. METHODS: Amniotic fluid was obtained in 29 consecutive patients admitted with the diagnosis of preterm PROM earlier than 35 weeks of gestation either by amniocentesis or by collecting cervical fluid. CRP was measured in maternal blood, amniotic fluid, vaginal fluid and in cord blood obtained at delivery. Intraamniotic infection was defined as a positive amniotic fluid for aerobic or anaerobic bacteria, or Mycoplasma. The placentas and umbilical cords were examined for the presence of chorioamnionitis and funisitis. RESULTS: A significant correlation was found between vaginal fluid CRP concentrations and both amniotic fluid (r = 0.95, p < 0.001) and umbilical cord levels (r = 0.47, p < 0.05). No correlation was found between maternal blood and vaginal fluid CRP concentrations. The proportion of patients with intraamniotic infection was 37.9% (11/29). The median (range) vaginal fluid CRP concentration was higher in patients with intraamniotic infection than in those with sterile amniotic fluid [901 (0-1354) vs. 507 (0-798) ng/mL, p < 0.001]. The median (range) vaginal fluid CRP concentration was higher in fetuses with (n = 12) than in those without funisitis (n = 17) [901 (598-1354) vs. 487 (0-1115) ng/mL, p < 0.01]. After adjustment for gestational age, vaginal fluid CRP concentration > 800 ng/mL remained a predictor of intraamniotic infection and funisitis. CONCLUSIONS: Increased vaginal fluid CRP concentration is associated with intraamniotic infection and funisitis. As CRP is produced by hepatocytes and does not cross the placenta, its measurement in vaginal fluid might be an additional parameter for the assessment of fetal well-being in patients with premature PROM.     

The relationship between cervical dilatation, interleukin-6 and interleukin-8 during term labor

BACKGROUND: To determine interleukin-6 and interleukin-8 levels in amniotic fluid, retroplacental blood and maternal serum and relate these values with cervical dilatation in term labor. METHODS: Prospective study. n=78 healthy women undergoing term cesarean section, divided into four groups: controls, n=42, (elective cesarean section; no contractions, membrane rupture or cervical dilatation); latent labor, n=12, (latent phase labor; cervix <2 cm dilated); established labor, n=12, (active labor, cervix 2-5 cm); advanced labor, n=12, (active labor, cervix >5 cm). Interleukin-6 and interleukin-8 were determined by ELISA (pg/ml), placenta and placental bed biopsy examined histopathologically, and amniotic fluid also microbiologically. Results were expressed as median and ranges or mean and standard deviations, as appropriate. For statistical analysis, Mann-Whitney U-tests or Kruskal-Wallis tests were used as applicable (Statview 4.5). Power and linear regression analyses were performed. p<0.05 was considered significant, p<0.001 highly significant. RESULTS: Compared with controls, IL-6 and IL-8 increased significantly with cervical dilatation in all compartments tested for almost all labor groups (p<0.05 to p<0.0001). Significant changes were also seen between latent and advanced labor groups in some compartments (p<0.05), but not between established and advanced labor groups. Intrauterine infection was excluded in any of the patients clinically and on histopathological or microbiological analysis of placentae and amniotic fluid. CONCLUSIONS: In term labor without intraamniotic infection, interleukin-6 and interleukin-8 at the fetomaternal interface and in maternal serum rise significantly with cervical dilatation. These cytokines could be used as markers of active labor if vaginal examination is not applicable.     

Increased amniotic fluid leukotriene C4 concentration in term human parturition

The purpose of this study was to determine whether parturition is associated with changes in the amniotic fluid concentration of leukotriene C4, an arachidonate lipoxygenase metabolite. Amniotic fluid was collected from 36 women not in labor and from 30 women in active labor with cervical dilation of greater than or equal to 6 cm. The concentration of leukotriene C4 was determined by radioimmunoassay. The median amniotic fluid concentration of leukotriene C4 was greater in laboring women than in nonlaboring women: 121 pg/ml (range, 52 to 261 pg/ml) versus 73.5 pg/ml (range, 6 to 249 pg/ml), respectively (p = 0.0008). These data are consistent with activation of the lipoxygenase pathway during spontaneous parturition at term.     

Infection and labor. IV. Cachectin-tumor necrosis factor in the amniotic fluid of women with intraamniotic infection and preterm labor

A growing body of evidence supports a causal link between subclinical intrauterine infection and preterm labor. The mechanisms responsible for the onset of parturition in this setting have not been elucidated. The conventional view has been that bacterial products increase prostaglandin biosynthesis by intrauterine tissues and this, in turn, leads to the onset of labor. An alternative or complementary mechanism is that microbial products activate the host monocyte-macrophage system and that cytokines released during this process signal the initiation of parturition by stimulating prostaglandin biosynthesis by intrauterine tissues. This study was conducted to determine if cachectin-tumor necrosis factor is present in the amniotic fluid of women with intraamniotic infection and whether this cytokine can alter the rate of prostaglandin biosynthesis by intrauterine tissues. Amniotic fluid from 54 women was assayed for tumor necrosis factor. Tumor necrosis factor was not detectable in the amniotic fluid of women without intraamniotic infection regardless of the presence or absence of term or preterm labor. On the other hand, the amniotic fluid of 11 of 15 women with preterm labor and intraamniotic infection had measurable tumor necrosis factor. This cytokine stimulated prostaglandin E2 biosynthesis by amnion cells in monolayer culture in a dose-dependent fashion. These data support the concept that macrophage activation is involved in the onset of human parturition in the setting of infection. We propose that the host (fetus and/or mother) signals the onset of parturition through the secretion of inflammatory cytokines released in response to bacterial invasion.     

Participation of the novel cytokine interleukin 18 in the host response to intra-amniotic infection

OBJECTIVE: Interleukin 18 is a proinflammatory pleiotropic cytokine that has been implicated in the host defense against infection. This study was undertaken to determine whether interleukin 18 concentrations change in the maternal, fetal, and amniotic fluid compartments with labor (term and preterm) and microbial invasion of the amniotic cavity. STUDY DESIGN: Amniotic fluid was assayed for interleukin 18 in samples obtained from 285 patients in the following groups: (1) term not in labor (n = 22), in labor (n = 19), and with microbial invasion of the amniotic cavity (n = 16); (2) preterm labor who delivered at term (n = 38), who delivered preterm but without microbial invasion of the amniotic cavity (n = 41), and preterm labor with microbial invasion of the amniotic cavity (n = 24); (3) preterm premature rupture of membranes without microbial invasion of the amniotic cavity (n = 30) and with microbial invasion of the amniotic cavity (n = 34); (4) term premature rupture of membranes not in labor (n = 20) and term premature rupture of membranes in labor (n = 19); and (5) midtrimester (n = 22). In addition, cord and maternal plasma samples from women at term not in labor (n = 20) and in labor (n = 20) were assayed for interleukin 18. RESULTS: (1) Interleukin 18 was detectable in all amniotic fluid samples and maternal and umbilical cord blood samples. (2) Interleukin 18 concentrations increased with advancing gestational age (r = 0.47; P <.0001). (3) Microbial invasion of the amniotic cavity in either preterm or term parturition was associated with a significant increase in the amniotic fluid concentration of interleukin 18 (preterm labor without microbial invasion of the amniotic cavity: median, 14.95 pg/mL; range, 3.9-277.0 pg/mL; vs preterm labor with microbial invasion of the amniotic cavity: median, 20.75 pg/mL; range, 5.53-160.21 pg/mL; P <.02; term labor without microbial invasion of the amniotic cavity: median, 18.73 pg/mL; range, 5.09-95.44 pg/mL; vs term labor with microbial invasion of the amniotic cavity: median, 24.35 pg/mL; range, 10.07-144.42 pg/mL; P<.004). (4) Both term and preterm parturition were associated with a modest increase in amniotic fluid interleukin 18 concentrations, although this trend did not reach statistical significance. (5) Rupture of membranes at term was associated with a significant decrease in amniotic fluid interleukin 18 concentrations (intact membranes: median, 14.96 pg/mL; range, <3.89-26.07 pg/mL; vs rupture of membranes: median, 10.1 pg/mL; range, 4.29-21.44 pg/mL; P <.001). CONCLUSION: (1) Interleukin 18 is increased in cases of microbial invasion of the amniotic cavity. (2) Interleukin 18 is detectable in the amniotic, maternal, and fetal compartments. (3) We propose that this novel cytokine plays a role in the host defense against infection.     

Amniotic fluid tumor necrosis factor-alpha is a marker for the prediction of early-onset neonatal sepsis in preterm labor

BACKGROUND: Our purpose was to determine whether amniotic fluid concentrations of tumor necrosis factor-alpha are of value in the prediction of early-onset neonatal sepsis (proven or suspected) in patients with preterm labor and intact membranes. METHODS: The relationship between amniotic fluid tumor necrosis factor-alpha concentrations and early-onset neonatal sepsis was examined in 59 consecutive patients with preterm labor and intact membranes who delivered preterm neonates within 72 h after transabdominal amniocentesis. Early-onset neonatal sepsis was defined either as the presence of a positive blood culture or as suspected sepsis within 72 h of delivery. Tumor necrosis factor-alpha was determined by enzyme-linked immunosorbent assays. RESULTS: Patients delivering neonates with early-onset neonatal sepsis had significantly higher median amniotic fluid TNF-alpha concentrations than patients delivering neonates without early-onset neonatal sepsis (p < 0.0005). An amniotic fluid tumor necrosis factor-alpha concentration > or =41 pg/ml had a sensitivity of 82% (23/29) and specificity of 79% (38/48) in the prediction of early-onset neonatal sepsis. Multiple logistic regression indicated that elevated amniotic fluid tumor necrosis factor-alpha (> or =41 pg/ml) was the only independent predictor of early-onset neonatal sepsis (odds ratio 12.9, 95% confidence interval 1.3-125.3, p=0.01) after correction for known confounding variables. CONCLUSIONS: (1) Amniotic fluid tumor necrosis factor-alpha is a marker for the prediction of early-onset neonatal sepsis in patients with preterm labor and intact membranes. (2) Amniotic fluid tumor necrosis factor-alpha is a better independent predictor of early-onset neonatal sepsis than placental histologic finding or amniotic fluid culture.     

Evidence of the involvement of caspase-1 under physiologic and pathologic cellular stress during human pregnancy: A link between the inflammasome and parturition

Objective. Caspase-1 is a component of the NALP3 inflammasome, a cytosolic multiprotein complex that mediates the processing of pro-inflammatory caspases and cytokines. The inflammasome represents the first line of defense against cellular stress and is a crucial component of innate immunity. Caspase-1 is the enzyme responsible for the cleavage and activation of interleukin (IL)-1β, which is a potent pro-inflammatory cytokine, and plays a central role in the mechanisms leading to labor (preterm and term) particularly in the context of intrauterine infection/inflammation. In addition, caspase-1 cleaves IL-18 and IL-33. The objectives of this study were to determine whether there is a relationship between amniotic fluid concentrations of caspase-1 and gestational age, parturition (term and preterm), and intra-amniotic infection/inflammation (IAI).

Study design. A cross-sectional study was conducted including 143 pregnant women in the following groups: (1) mid-trimester of pregnancy (n = 18); (2) term not in labor (n = 25); (3) term in labor (n = 28); (4) preterm labor (PTL) who delivered at term (n = 23); (5) PTL without IAI who delivered preterm (n = 32); (6) PTL with IAI who delivered preterm neonates (n = 17). Caspase-1 concentrations in amniotic fluid were determined by a specific and sensitive immunoassay. Non-parametric statistics were used for analysis.

Results. (1) Caspase-1 was detected in amniotic fluid of women at term, but in none of the mid-trimester samples. (2) Patients in labor at term had a significantly higher median amniotic fluid concentration of caspase-1 than women at term not in labor (term in labor: 10.5 pg/mL, range 0.0–666.0 vs. term not in labor: 5.99 pg/mL, range 0.0–237.4; p < 0.05). (3) Among patients with spontaneous PTL, those with IAI (median 41.4 pg/mL, range 0.0–515.0) had a significantly higher median amniotic fluid caspase-1 concentration than those without IAI who delivered preterm (median 0.0 pg/mL, range 0.0–78.4) and than those who delivered at term (median 0.0 pg/mL, range 0.0–199.5); p < 0.001 for both comparisons.

Conclusions. (1) The presence and concentration of caspase-1 in the amniotic fluid varies as a function of gestational age. (2) Women with spontaneous labor at term had a higher median caspase-1 amniotic fluid concentration than women at term without labor. This suggests that the inflammasome may be activated in spontaneous parturition at term. Since most women with labor do not have intra-amniotic infection, we propose that cellular stress during labor accounts for activation of the inflammasome. (3) Preterm labor associated with infection/inflammation was also associated with a high concentration of caspase-1, suggesting that infection may induce caspase-1 production and activation of the inflammasome. (4) The sequential activation of the inflammasome and caspase-1, leading to interleukin-1β processing and secretion, is a candidate pathway leading to the activation of the common pathway of parturition.