Clinical chorioamnionitis--an ongoing obstetrical conundrum

Should the diagnostic criteria for suspected clinical chorioamnionitis be changed?

Purpose of review: The criteria for the diagnosis of intra-amniotic infection (IAI) were derived from a study of women at term in labor but is currently used as the main diagnostic tool for clinical chorioamnionitis. Regarding the inconsistent usage of the term, the diagnostic utility of clinical chorioamnionitis needs to be revisited. In this review, we addressed the critical issues on why the diagnostic criteria of suspected clinical chorioamnionitis should be changed.Recent findings: Overall, the accuracy of clinical chorioamnionitis to detect intra-amniotic infection (IAI) is not high, around 50%. The accuracy of each diagnostic criteria to diagnose IAI is, for example, 51.1% with maternal tachycardia, 57.8% with fetal tachycardia, and 55.6% with maternal leukocytosis. However, it needs to be reminded that these diagnostic performances had been obtained from term pregnancies but not from preterm pregnancies. Since there is a difference between clinical chorioamnionitis and histologic chorioamnionitis or even IAI, the diagnostic criteria of clinical chorioamnionitis would be ideal if it could directly predict the development of neonatal infectious outcomes. In fact, multiple definitions of clinical chorioamnionitis either in more lenient or stringent manner are currently used, which is responsible for inconsistent association of clinical chorioamnionitis with long-term neonatal outcomes. Whereas the diagnosis of clinical chorioamnionitis in preterm is followed by expeditious delivery, the diagnosis of clinical chorioamnionitis at term pregnancy is usually conducted in laboring women and requires additional neonatal evaluation for sepsis, which suggests different implications of clinical chorioamnionitis in preterm and term pregnancy.Summary: Current diagnostic criteria of clinical chorioamnionitis should be revised, specifically in terms of sensitivity in preterm pregnancy and specificity in term pregnancy.

Clinical chorioamnionitis at term IX: in vivo evidence of intra-amniotic inflammasome activation

Background The inflammasome has been implicated in the mechanisms that lead to spontaneous labor at term. However, whether the inflammasome is activated in the amniotic cavity of women with clinical chorioamnionitis at term is unknown. Herein, by measuring extracellular ASC [apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (CARD)], we investigated whether there is in vivo inflammasome activation in amniotic fluid of patients with clinical chorioamnionitis at term with sterile intra-amniotic inflammation and in those with intra-amniotic infection. Methods This was a retrospective cross-sectional study that included amniotic fluid samples collected from 76 women who delivered after spontaneous term labor with diagnosed clinical chorioamnionitis. Intra-amniotic inflammation was defined as an elevated amniotic fluid interleukin (IL)-6 concentration ≥2.6 ng/mL, and intra-amniotic infection was diagnosed by the presence of microbial invasion of the amniotic cavity (MIAC) accompanied by intra-amniotic inflammation. Patients were classified into the following groups: (1) women without intra-amniotic inflammation or infection (n=16); (2) women with MIAC but without intra-amniotic inflammation (n=5); (3) women with sterile intra-amniotic inflammation (n=15); and (4) women with intra-amniotic infection (n=40). As a readout of in vivo inflammasome activation, extracellular ASC was measured in amniotic fluid by enzyme-linked immunosorbent assay. Acute inflammatory responses in the amniotic fluid and placenta were also evaluated. Results In clinical chorioamnionitis at term: (1) amniotic fluid concentrations of ASC (extracellular ASC is indicative of in vivo inflammasome activation) and IL-6 were greater in women with intra-amniotic infection than in those without intra-amniotic inflammation, regardless of the presence of MIAC; (2) amniotic fluid concentrations of ASC and IL-6 were also higher in women with sterile intra-amniotic inflammation than in those without intra-amniotic inflammation, regardless of the presence of MIAC; (3) amniotic fluid concentrations of IL-6, but not ASC, were more elevated in women with intra-amniotic infection than in those with sterile intra-amniotic inflammation; (4) a positive and significant correlation was observed between amniotic fluid concentrations of ASC and IL-6; (5) no differences were observed in amniotic fluid ASC and IL-6 concentrations between women with and without MIAC in the absence of intra-amniotic inflammation; (6) women with intra-amniotic infection had elevated white blood cell counts and reduced glucose levels in amniotic fluid compared to the other three study groups; and (7) women with intra-amniotic infection presented higher frequencies of acute maternal and fetal inflammatory responses in the placenta than those with sterile intra-amniotic inflammation. Conclusion The intra-amniotic inflammatory response, either induced by alarmins or microbes, is characterized by the activation of the inflammasome - as evidenced by elevated amniotic fluid concentrations of extracellular ASC - in women with clinical chorioamnionitis at term. These findings provide insight into the intra-amniotic inflammatory response in women with clinical chorioamnionitis at term.

Does the human placenta delivered at term have a microbiota? Results of cultivation, quantitative real-time PCR, 16S rRNA gene sequencing, and metagenomics

BACKGROUND

The human placenta has been traditionally viewed as sterile, and microbial invasion of this organ has been associated with adverse pregnancy outcomes. Yet, recent studies that utilized sequencing techniques reported that the human placenta at term contains a unique microbiota. These conclusions are largely based on the results derived from the sequencing of placental samples. However, such an approach carries the risk of capturing background-contaminating DNA (from DNA extraction kits, polymerase chain reaction reagents, and laboratory environments) when low microbial biomass samples are studied.

OBJECTIVE

To determine whether the human placenta delivered at term in patients without labor who undergo cesarean delivery harbors a resident microbiota ("the assemblage of microorganisms present in a defined niche or environment").

STUDY DESIGN

This cross-sectional study included placentas from 29 women who had a cesarean delivery without labor at term. The study also included technical controls to account for potential background-contaminating DNA, inclusive in DNA extraction kits, polymerase chain reaction reagents, and laboratory environments. Bacterial profiles of placental tissues and background technical controls were characterized and compared with the use of bacterial culture, quantitative real-time polymerase chain reaction, 16S ribosomal RNA gene sequencing, and metagenomic surveys.

RESULTS

(1) Twenty-eight of 29 placental tissues had a negative culture for microorganisms. The microorganisms retrieved by culture from the remaining sample were likely contaminants because corresponding 16S ribosomal RNA genes were not detected in the same sample. (2) Quantitative real-time polymerase chain reaction did not indicate greater abundances of bacterial 16S ribosomal RNA genes in placental tissues than in technical controls. Therefore, there was no evidence of the presence of microorganisms above background contamination from reagents in the placentas. (3) 16S ribosomal RNA gene sequencing did not reveal consistent differences in the composition or structure of bacterial profiles between placental samples and background technical controls. (4) Most of the bacterial sequences obtained from metagenomic surveys of placental tissues were from cyanobacteria, aquatic bacteria, or plant pathogens, which are microbes unlikely to populate the human placenta. Coprobacillus, which constituted 30.5% of the bacterial sequences obtained through metagenomic sequencing of placental samples, was not identified in any of the 16S ribosomal RNA gene surveys of these samples. These observations cast doubt as to whether this organism is really present in the placenta of patients at term not in labor.

CONCLUSION

With the use of multiple modes of microbiologic inquiry, a resident microbiota could not be identified in human placentas delivered at term from women without labor. A consistently significant difference in the abundance and/or presence of a microbiota between placental tissue and background technical controls could not be found. All cultures of placental tissue, except 1, did not yield bacteria. Incorporating technical controls for potential sources of background-contaminating DNA for studies of low microbial biomass samples, such as the placenta, is necessary to derive reliable conclusions.

The frequency and clinical significance of intra-amniotic inflammation in twin pregnancies with preterm labor and intact membranes

OBJECTIVE

The objective of this study is to evaluate the frequency and clinical significance of intra-amniotic inflammation in twin pregnancies with preterm labor and intact membranes.

STUDY DESIGN

Amniotic fluid (AF) was retrieved from both sacs in 90 twin gestations with preterm labor and intact membranes (gestational age between 20 and 34 6/7 weeks). Preterm labor was defined as the presence of painful regular uterine contractions, with a frequency of at least 2 every 10 min, requiring hospitalization. Fluid was cultured and assayed for matrix metalloproteinase-8. Intra-amniotic inflammation was defined as an AF matrix metalloproteinase-8 concentration >23 ng/mL.

RESULTS

The prevalence of intra-amniotic inflammation for at least 1 amniotic sac was 39% (35/90), while that of proven intra-amniotic infection for at least one amniotic sac was 10% (9/90). Intra-amniotic inflammation without proven microbial invasion of the amniotic cavity was found in 29% (26/90) of the cases. Intra-amniotic inflammation was present in both amniotic sacs for 22 cases, in the presenting amniotic sac for 12 cases, and in the non-presenting amniotic sac for one case. Women with intra-amniotic inflammation observed in at least one amniotic sac and a negative AF culture for microorganisms had a significantly higher rate of adverse pregnancy outcome than those with a negative AF culture and without intra-amniotic inflammation (lower gestational age at birth, shorter amniocentesis-to-delivery interval, and significant neonatal morbidity). Importantly, there was no significant difference in pregnancy outcome between women with intra-amniotic inflammation and a negative AF culture and those with a positive AF culture.

CONCLUSION

Intra-amniotic inflammation is present in 39% of twin pregnancies with preterm labor and intact membranes and is a risk factor for impending preterm delivery and adverse outcome, regardless of the presence or absence of bacteria detected using cultivation techniques.

Clinical chorioamnionitis at term VIII: a rapid MMP-8 test for the identification of intra-amniotic inflammation

OBJECTIVE

Clinical chorioamnionitis is the most common infection/inflammatory process diagnosed in labor and delivery units worldwide. The condition is a syndrome that can be caused by (1) intra-amniotic infection, (2) intra-amniotic inflammation without demonstrable microorganisms (i.e. sterile intra-amniotic inflammation), and (3) maternal systemic inflammation that is not associated with intra-amniotic inflammation. The presence of intra-amniotic inflammation is a risk factor for adverse maternal and neonatal outcomes in a broad range of obstetrical syndromes that includes clinical chorioamnionitis at term. Although the diagnosis of intra-amniotic infection has relied on culture results, such information is not immediately available for patient management. Therefore, the diagnosis of intra-amniotic inflammation could be helpful as a proxy for intra-amniotic infection, while results of microbiologic studies are pending. A rapid test is now available for the diagnosis of intra-amniotic inflammation, based on the determination of neutrophil collagenase or matrix metalloproteinase-8 (MMP-8). The objectives of this study were (1) to evaluate the diagnostic indices of a rapid MMP-8 test for the identification of intra-amniotic inflammation/infection in patients with the diagnosis of clinical chorioamnionitis at term, and (2) to compare the diagnostic performance of a rapid MMP-8 test to that of a conventional enzyme-linked immunosorbent assay (ELISA) interleukin (IL)-6 test for patients with clinical chorioamnionitis at term.

MATERIALS AND METHODS

A retrospective cohort study was conducted. A transabdominal amniocentesis was performed in patients with clinical chorioamnionitis at term (n=44). Amniotic fluid was analyzed using cultivation techniques (for aerobic and anaerobic bacteria as well as genital Mycoplasmas) and broad-range polymerase chain reaction (PCR) coupled with electrospray ionization mass spectrometry (PCR/ESI-MS). Amniotic fluid IL-6 concentrations were determined by ELISA, and rapid MMP-8 results were determined by Yoon's MMP-8 Check®. Intra-amniotic inflammation was defined as an elevated amniotic fluid IL-6 concentration ≥2.6 ng/mL, and intra-amniotic infection was diagnosed by the presence of microorganisms in the amniotic fluid accompanied by intra-amniotic inflammation. The diagnostic indices of Yoon's MMP-8 Check® for the identification of intra-amniotic inflammation were calculated. In order to objectively compare Yoon's MMP-8 Check® with the ELISA IL-6 test for the identification of intra-amniotic inflammation, we used an amniotic fluid white blood cell (WBC) count ≥50 cells/mm3 to define intra-amniotic inflammation.

RESULTS

(1) A positive rapid MMP-8 test had a sensitivity of 82.4% (28/34), specificity of 90% (9/10), positive predictive value of 96.6% (28/29), negative predictive value of 60% (9/15), positive likelihood ratio 8.2 (95% CI 1.3-53.2), and negative likelihood ratio 0.2 (95% CI 0.1-0.4) for the identification of intra-amniotic inflammation (prevalence 77.3%); (2) a positive rapid MMP-8 test had a sensitivity of 91.7% (22/24), specificity of 65% (13/20), positive predictive value of 75.9% (22/29), negative predictive value of 86.7% (13/15), positive likelihood ratio of 2.6 (95% CI 1.4-4.8), and negative likelihood ratio of 0.1 (95% CI 0.03-0.5) for the identification of intra-amniotic infection; (3) the rapid MMP-8 test had a significantly higher specificity than the ELISA IL-6 test in the identification of intra-amniotic inflammation as determined by an amniotic fluid WBC count ≥50 cells/mm3. The sensitivity and accuracy of the rapid MMP-8 test were comparable to those of the ELISA IL-6 test; and (4) importantly, the rapid MMP-8 test had 100% sensitivity and 100% negative predictive value in the identification of neonates affected with fetal inflammatory response syndrome (FIRS).

CONCLUSION

The rapid diagnosis of intra-amniotic inflammation is possible by analysis of amniotic fluid using a point-of-care test for MMP-8. Patients with a positive test are at risk of delivering a neonate affected with systemic inflammation, a risk factor for adverse neonatal outcome.

Clinical chorioamnionitis at term VII: the amniotic fluid cellular immune response

OBJECTIVES

1) To characterize the cellular composition of the amniotic fluid of patients diagnosed with clinical chorioamnionitis at term, as a function of the presence or absence of microorganisms determined by cultivation techniques, and 2) to characterize the cytokine production by white blood cells present in the amniotic fluid using flow cytometry-based techniques.

MATERIALS AND METHODS

Amniotic fluid samples from 20 women who had the diagnosis of clinical chorioamnionitis at term were analyzed using cultivation techniques (for aerobic and anaerobic bacteria as well as genital Mycoplasmas). Amniotic fluid IL-6 concentrations were determined by an enzyme-linked immunosorbent assay. Amniotic fluid leukocytes were visualized by using hematoxylin and eosin staining and immunofluorescence. Immunophenotyping of surface markers and cytokines was performed in amniotic fluid leukocytes using flow cytometry.

RESULTS

1) Neutrophils (CD45+CD15+ cells) were the most common leukocyte subset found in the amniotic fluid, followed by monocytes (CD45+CD14+ cells); other white blood cells (such as lymphocytes and natural killer cells) were scarce in the amniotic fluid; 2) the absolute counts of neutrophils and monocytes were significantly higher in patients with microorganisms found in the amniotic fluid than in those without detectable microorganisms, using cultivation techniques; 3) there was a significant correlation between the absolute counts of neutrophils and monocytes determined by flow cytometry (Spearman's correlation=0.97; P<0.001); 4) there was a significant correlation between the absolute white blood cell count determined with a hemocytometer chamber and by flow cytometric analysis (Spearman's correlation=0.88; P<0.001); and 5) the profile of cytokine expression differed between monocytes and neutrophils; while neutrophils predominantly produced TNF-α and MIP-1β, monocytes expressed higher levels of IL-1β and IL-1α.

CONCLUSION

Flow cytometry analysis of the amniotic fluid of patients with intra-amniotic infection and clinical chorioamnionitis at term demonstrated that neutrophils and monocytes are the most common cells participating in the inflammatory process. We have characterized, for the first time, the differential cytokine expression by these cells in this important complication of pregnancy.