preterm birth is due to several causes , among which a   preexisting  occasionally 
 asymptomatic  intrauterine infection relatively early in 
 pregnancy should be considered [ 13 ] .
thus , amniotic 
 fluid microbial invasion [ 1 , 2 , 4 , 5 ] and/or elevated levels of proinflammatory cytokines , chemokines , or other implicated molecules [ 3 , 4 , 6 , 7 ] should be investigated .
elastase , a protease produced by neutrophils , histiocytes , and 
 macrophages , is stored in cytoplasmic granules and is secreted 
 during cell activation .
it targets at the degradation of intra- or 
 extracellular proteins , among which elastin , collagen , and 
 fibronectin [ 8 , 9 ] are included .
main inhibitor of elastase 
 is the secretory leukocyte proteinase inhibitor ( slpi ) , present in 
 the secretions of the respiratory and genital system [ 1012 ] .
it has been shown that slpi limits the proinflammatory 
 cascades ongoing during parturition , protects against microbial 
 invasion and the response to infection , and inhibits the proinflammatory action of bacterial products , for instance of 
 lipopolysaccharides [ 14 , 15 ] .
in general , protease inhibitors , by controlling extracellular matrix proteolysis , contribute to tissue homeostasis .
increased elastase concentrations have been documented at the site 
 of ruptured membranes in cases of preterm delivery .
the ratio of elastase to spli concentrations is important for the 
 evolution of a normal delivery , as spli seems to protect both 
 fetal membranes and cervical tissue .
adhesion molecules ( soluble intercellular adhesion molecule 
 ( sicam-1 ) and soluble vascular cell adhesion molecule 
 ( svcam-1 ) ) are members of the cell - surface immunoglobulin 
 superfamily of adhesion receptors   expressed on haematopoietic and nonhaematopoietic cell surfaces , 
 particularly on endothelial cells   and induced or upregulated by proinflammatory cytokines ( eg , interleukin-1 , 
 tumor necrosis factor  , interferon- ) [ 20 , 21 ] .
as they mediate the adhesion of lymphocytes , monocytes , and 
 eosinophils on activated endothelium , they enable circulating 
 white cells to enter inflamed tissues [ 22 , 23 ] , and thus they 
 are used as markers of inflammation or tissue damage . 

both molecules exist in transmembrane and soluble ( s ) forms 
 [ 25 , 26 ] .
this study was based on the hypothesis that elevated midtrimester 
 amniotic fluid concentrations of elastase , sicam-1 , svcam-1 , 
 and decreased levels of slpi ( all four substances are implicated 
 in the inflammatory process ) could possibly serve as useful 
 predictors of asymptomatic intra - amniotic inflammation and/or 
 infection , eventually resulting in preterm labor and delivery
. 
 therefore , we aimed to determine the above substances in the 
 amniotic fluid of women , undergoing second trimester amniocentesis 
 and subsequently delivering pre- or full - term infants .
three hundred and twelve women at the second trimester of 
 pregnancy underwent ultrasound  guided transabdominal 
 amniocentesis for several reasons ( advanced maternal age , nuchal 
 translucency of the fetus , family history of congenital anomalies , 
 parental hemoglobinopathies ) .
these women belonged to a low - risk 
 pregnancy group , as stated by their private obstetricians , who 
 followed them on a regular basis .
out of the total 312 women , 
 13 subsequently progressed to spontaneous preterm delivery 
 before 37 weeks of gestation , 6 with and 7 without rupture 
 of membranes .
the above 13 women were matched for maternal age , 
 parity , and gestational age at amniocentesis ( within 2 weeks ) 
 with all eligible controls ( 21 out of the initial 312 women ) , 
 who delivered at 37 weeks of gestation or later 
 healthy , appropriate for gestational age neonates ( all with birth weights between the 30th and 70th customized centile - controlling for maternal height , 
 booking weight , ethnic group , parity , gestational age , birth 
 weight , and neonatal gender ) .
premature rupture of membranes , defined as leaking of amniotic fluid before the onset 
 of labor , was absent in 12 and present in 9 out of these 21 controls with term delivery .
women with multiple pregnancy , cervical dilatation ( > 1 cm , 
 or ruptured membranes at the time of amniocentesis , abnormal fetal 
 karyotype , or major fetal anomalies were excluded .
all included in 
 this study cases and controls were nonsmokers and did not report a 
 previous preterm delivery .
neither clinical signs of 
 chorioamnionitis ( temperature  37.8c , uterine 
 tenderness , malodorous vaginal discharge , fetal tachycardia 
 > 160 beats / min , maternal tachycardia > 100 beats / min , 
 and maternal leucocytosis > 15000 cells / mm ) nor 
 bleeding during pregnancy was reported .
the ethical 
 committee of our teaching hospital approved the collection and the 
 use of these samples . written informed consent
drawn amniotic fluid was centrifuged and stored in polypropylene 
 tubes at 80c until assay .
levels of all substances 
  were determined by commercially   available enzyme - linked immunosorbent assays : polymorphonuclear ( pmn ) elastase , by immundiagnostik ag ( d-64625 , bensheim ) , human slpi , human sicam-1 , and human svcam-1 , r&d systems inc . 

sensitivity , intra- and interassay 
 coefficients of variation for pmn elastase were < 0.12 ng / ml , 
 7.5% and 8.4% ; for spli < 25
pg / ml , 4.5% and 
 6.2% ; for sicam-1 0.35 ng / ml , 3.5% and 
 5.9% ; and for svcam-1 2 ng / ml , 6.3% and 
 8.2% , respectively .
as data from all four substances were normally distributed 
 ( kolmogorov - smirnov test ) , t 
 test was applied for the comparison 
 of investigated amniotic fluid substances between pre- and 
 full - term pregnancies .
nonparametric tests were applied for the 
 comparisons between intact and ruptured membranes in each group . 

p < .05 was considered statistically significant . a receiver - operating characteristic ( roc ) curve was used to identify cutoff concentrations of amniotic fluid elastase , spli , sicam-1 , 
 and svcam-1 for spontaneous preterm delivery after midtrimester amniocentesis .
pmn elastase , sicam-1 , and 
 svcam-1 levels were higher and slpi levels were lower in 
 second - trimester amniotic fluid of mothers delivering preterm as 
 compared to mothers delivering at term , however , these findings 
 did not reach statistical significance .
in contrast , slpi levels 
 in second - trimester amniotic fluid were significantly higher in 
 the group of women who delivered either preterm ( p < .007 ) or at 
 term ( p < .001 ) with absence of ruptured membranes prior to 
 delivery ( see figure 1 ) . furthermore , a statistical 
 significant correlation existed between elastase and spli 
 ( r = 0.508 , p < .002 ) .
roc curve analysis of delivery at < 37 weeks for various cutoff levels of elastase , slpi , sicam-1 , and svcam-1 was performed . the best cutoff point for 
 elastase
was a concentration of 5.72 ng / ml ( sensitivity 53.8% , specificity 57.14% , odds ratio ( or ) 1.6 , 95% confidence interval 
 ( ci ) = 0.4 - 6.3 ) , 
 for spli a concentration of 56.5 ng / ml ( sensitivity 
 53.8% , specificity 42.86% , or = 0.9 , 95% ci = 0.2 - 3.5 ) , for sicam-1 a concentration of 116 ng / ml , ( sensitivity 62% , 
 specificity 62% , or 2.6 , 95% ci : 0.6 - 10.8 ) , and for svcam-1 a concentration of 
 290 g / dl , ( sensitivity 76.9% , specificity 
 57.1% , or 4.4 , 95% ci = 0.9 - 21 ) .
in this study we prospectively determined midtrimester amniotic 
 fluid concentrations of several factors and related their levels 
 with pregnancy outcome .
our results indicate that even from the 
 early second trimester of pregnancy , in preterm or full - term 
 deliveries , preceded by rupture of membranes , levels of slpi are 
 significantly decreased , possibly implying influence of the latter 
 on membrane integrity .
previous studies have reported that amniotic fluid protease 
 inhibitors [ alpha 1-protease inhibitor ( 1 -pi ) , urinary 
 trypsine inhibitor , and slpi ] control elastase activity 
 [ 12 , 13 , 28 , 29 ] . in this respect ,
amniotic fluid concentrations of 
 1 -pi have been found lower in women with rupture of 
 membranes .
in addition , zhang et al   reported 
 that slpi functions as a potent anti - inflammatory agent by 
 interfering with the signal transduction pathway leading to 
 production of monocyte matrix metalloproteinases , which are also 
 implicated in membrane rupture . on the other hand , the adverse 
 effects of elastase on the growth and properties of elastic tissue 
 in the amnion of rabbits have been demonstrated . 

relatively , immunohistochemical studies of fetal ruptured 
 membranes have shown accumulation of elastase at the ruptured site 
 both in full- and preterm deliveries [ 32 , 33 ] .
amniotic fluid neutrophils are of fetal origin and accumulation of 
 elastase in the amniotic fluid could reflect fetal inflammatory response , as it happens with respective increase of metalloproteinase 8 .
a possible explanation for the lower slpi concentrations in cases of ruptured membranes is its consumption 
 early in pregnancy during repeated inflammatory processes . on the 
 other hand
, the determination in the amniotic fluid of elastase 
 both in pre- and full - term delivery could imply that this 
 substance is part of the common metabolic pathway of labour , and 
 therefore its concentrations did not change significantly in both 
 groups of the study .
concerning adhesion molecules , previous studies have shown that 
 increased circulating sicam-1 levels in midtrimester amniotic 
 fluid are related to a shortened length of gestation at delivery 
 , that intercellular adhesion molecule-1 concentration , in utero , decreases after antibiotic treatment   and that 
 determination of sicam-1 , expressed on fetal membranes and 
 mononuclear cells of amniotic fluid , may be a valuable biomarker 
 for early detection of acute chorioamnionitis and the possibility 
 of premature rupture of membranes .
nevertheless , another study states that in contrast to other proinflammatory molecules 
 ( interleukin-6 and leukocyte adhesion molecule-1 ) , amniotic 
 fluid sicam-1 concentrations were not significantly different 
 between patients with intra - amniotic infection than without intra - amniotic infection , a finding being in accordance with the relevant result of the present study , referring to incidence of preterm delivery .
lastly , to the best of our knowledge , no study could be found 
 determining amniotic fluid concentrations of svcam-1 in 
 midtrimester . in conclusion ,
second - trimester amniotic fluid slpi levels are 
 significantly decreased in cases where pre- or full - term delivery 
 is preceded by membrane rupture .
therefore , slpi concentrations in 
 the amniotic fluid obtained by second - trimester amniocentesis 
 could possibly predict the rupture of membranes either in the 
 second or in the third trimester .
in contrast , based on this 
 study , midtrimester amniotic fluid elastase , slpi , sicam-1 , and 
 svcam-1 concentrations are not helpful in predicting preterm 
 delivery .
levels of slpi in women , who delivered either preterm ( a ) 
 or at term ( b ) with intact membranes ( a ) 
 n = 7 and ( b ) n = 12 or premature rupture of membranes 
 ( prom ) ( a ) n = 6 and ( b ) n = 9 , respectively .
demographic data of participating women delivering at 
 < 37 weeks of gestation ( cases ) or at term ( controls ) ( mean  sd ) .
 aims . our aim is to investigate , in 13 cases 
 ( delivering preterm ) and 21 matched ( for age , parity , and 
 gestational age ) controls ( delivering at term ) , whether 
 midtrimester amniotic fluid concentrations of elastase , secretory 
 leukocyte proteinase inhibitor ( slpi ) , soluble intercellular 
 adhesion molecule-1 , and soluble vascular cell adhesion molecule 
 predict asymptomatic intra - amniotic inflammation / infection and 
 preterm labor . results . 
 concentrations of all substances 
 were not statistically different among mothers , delivering preterm 
 or at term . 
 slpi concentrations significantly increased in women , 
 going into labor without ruptured membranes , irrespective of pre- 
 or term delivery ( p < .007 , p < .001 , resp ) and correlated with 
 elastase ( r =   0.508 , p < .002 ) . 
 conclusions . 
 midtrimester amniotic fluid slpi concentrations significantly decrease when 
 membrane rupture precedes pre- or full - term labor . 
 however , none 
 of the investigated substances predict preterm delivery . 