In the quantitative analysis of inflammatory cytokines and regulators of amniotic fluid collected at delivery, cervical ureaplasma colonization was significantly associated with intraamniotic inflammation in preterm labor with intact membrane.
According to recommendations of the American College of Obstetricians and Gynecologists, intraamniotic infection or chorioamnionitis, which is defined as an infection with resulting inflammation of any combination of amniotic fluid, placenta, fetal membranes, or decidua, can be established by amniotic fluid culture, gram stain, or both accompanied with biochemical analysis . However, chorioamnionitis can be subclinical, which is defined histologically by inflammation of the chorion, amnion, and placenta . In consideration of these limitations, we further analyzed the histologically proven chorioamnionitis as well as inflammatory cytokines and regulators derived in amniotic fluid.
The microorganisms that were most commonly associated with infection of the amniotic cavity were the species of ureaplasma urealyticum, ureaplasma parvum, mycoplasma hominis, et al [27, 28]. To investigate the association between inflammatory cytokines and regulators of the amniotic fluid and cervical ureaplasma colonization, 27 cases which were colonized with other organisims (mycoplasma, chlamydia, and trichomonas) were excluded from the present study.
Previous studies have already reported a positive relationship between inflammatory cytokines (IL-6, MMP-8) of the amniotic fluid and the stage of histologic inflammation of the placenta in preterm birth [5, 29, 30]. In the present study, cervical ureaplasma colonization was significantly associated with the incidence of histologic chorioamnionitis in preterm birth. In particular, increased IL-10, MMP-8, and MMP-9 concentrations in the amniotic fluid of the ureaplasma positive group were significantly increased in those who experienced preterm labor with intact membrane. These findings might partially support the role of cervical ureaplasma colonization as a risk factor for chorioamnionitis and preterm birth [31, 32]. However, other studies that have demonstrated that ureaplasma colonization in the lower genital tract is not a significant predictor of preterm birth or chorioamnionitis [33–35]. In these reasons, it was difficult to confirm the role of ureaplasma as a causative agent of chorioamnionitis .
Unlike pro-inflammatory cytokines, such as IL-1β, IL-6, IL-8, and TNF-α, IL-10 dampens inflammation. Gotsch et al. reported that IL-10 concentration in amniotic fluid is elevated in spontaneous term and preterm labor as well as intraamniotic infection . MMPs lead to degradation of extracellular matrix components and modulation of cytokines, which may play an important role in spontaneous labor as well as intraamniotic infection [10, 11]. In the present study, intraamniotic infection-associated biomarkers of amniotic fluid collected at delivery, including IL-10, MMP-8, and MMP-9, was significantly different according to the presence or absence of cervical ureaplasma colonization.
There was inversely proportional between intraamniotic inflammation and gestational age [7–9, 24, 25]. In the present study, mean gestational age at delivery in histologic chorioamnionitis was lower, mean values of inflammatory cytokines and regulators was negatively correlated with gestational age at delivery.
Similar to the findings in previous studies [19, 20], ureaplasma parvum was more frequent in lower genital tract than ureaplasma urealyticum. ureaplasma parvum was more frequent in the lower genital tract than ureaplasma urealyticum. In the present study, there were no significant differences in the concentrations of chorioamnionitis-associated cytokines between cases with ureaplasma parvum and those with ureaplasma urealyticum. However, due to the small number of cases with ureaplasma urealyticum included in our study, it is impossible to determine a difference between ureaplasma parvum and ureaplasma urealyticum solely from our results.
Apart from biochemical chorioamnionitis by quantitative analysis of inflammatory cytokines and regulators of amniotic fluid, we performed a multivariate logistic regression analysis to determine whether cervical ureaplasma colonization is a risk factor for histologic chorioamnionitis. Although there was no significant difference between histologic chorioamnionitis and preterm labor with intact membrane or PPROM in two-by-two analysis, preterm labor with intact membrane and PPROM were included in the multivariate logistic regression analysis, considering previous studies [6–9, 24, 25]. After adjusted by preterm labor with intact membrane, PPROM, and gestational age at delivery, cervical ureaplasma colonization was an independent risk factor of histologic chorioamnionitis in the present study.
A particular strength of the present study includes the method of amniocentesis. In previous studies, amniocentesis was conducted via ultrasound-guided transabdominal approach [7, 9, 29, 30, 36–38]. Although ultrasound guidance for amniocentesis is not associated with amniocentesis-attributable complications, such as preterm labor, placental abruption, PPROM, and fetal heart rate abnormality , the possibility of emergent cesarean delivery after amniocentesis is a major complication to be considered during third-trimester amniocentesis [40, 41]. Considering the possibility of complications caused by ultrasound-guided transabdominal amniocentesis, we collected amniotic fluid when the amniotic sac was exposed during cesarean section. In a previous study on pregnant women who made it to full term with intact membranes, amniotic fluid was retrieved by puncture under direct visualization after uterine incision at the time of cesarean section . However, in our study, more than 50% of enrolled pregnant women experienced preterm labor, and the mean gestational age at delivery was 31.5 weeks.
The limitations of the present study are as follows: At first, although Administration of intrapartum antibiotics is recommended whenever an intraamniotic infection is suspected, there were no investigations related to antibiotic use. This study was conducted in a single tertiary institution, but it was difficult to investigate the use of antibiotics, the type of antibiotics, and the duration of antibiotic administration in the pregnant women who were recruited from secondary medical institutions. Second, other microorganisms including gardnerella vaginalis, group B Streptococcus, candida albicans were not investigated. Additional studies with larger population sizes are needed to clarify the association between chorioamnionitis-associated cytokines in amniotic fluid and cervical ureaplasma colonization in preterm delivery.
Although a causative relationship between cervical ureaplasma colonization and intraamniotic infection in preterm birth is impossible to conclusively determine, cervical ureaplasma colonization augments biochemically intraamniotic inflammation in preterm labor with intact membrane, and was an independent risk factor of histologic chorioamnionitis.