Cervical length and gestational age at admission as predictors of intra-amniotic inflammation in preterm labor with intact membranes.

OBJECTIVES: To evaluate cervical length and gestational age as predictors of intra-amniotic inflammation in patients admitted because of preterm labor and intact membranes.
METHODS: Ninety-three pregnant women with preterm labor and intact membranes were included in our study. Cervical length was measured on admission by transvaginal sonography and transabdominal amniocentesis was performed within the first 48 h following admission. Positive amniotic fluid cultures defined intra-amniotic infection. Levels of intra-amniotic interleukin-6 (IL-6) were measured, and a receiver-operating characteristics (ROC) curve was constructed to determine the best cut-off point of IL-6 for predicting intra-amniotic infection. This value was then used as a basis for determining a cut-off of IL-6 for defining intra-amniotic inflammation. Considering inflammatory status, perinatal outcomes were evaluated and compared. Logistic regression was used to investigate associations of different explanatory variables with inflammatory status. A non-invasive approach for detection of intra-amniotic inflammation in women admitted because of preterm labor with intact membranes was evaluated.
RESULTS: Intra-amniotic infection and inflammation rates were 14% and 28%, respectively. ROC curve analysis showed that the best cut-off value for IL-6 was 13.4 ng/mL for predicting intra-amniotic infection, which was comparable to the cut-off of 11.3 ng/mL reported previously by other authors (which we used to define inflammation). Regardless of the intra-amniotic microbial status, perinatal outcomes in women who developed intra-amniotic inflammation were worse than in those who did not. Cervical length < 15 mm and gestational age at admission < 28 weeks were independently associated with intra-amniotic inflammation. A strategy considering these two non-invasive parameters (either women admitted < 28 weeks or women admitted between >or= 28 and < 32 weeks with a cervical length < 15 mm) could detect 84.0% of women with intra-amniotic inflammation with a positive predictive value of 48.8%, providing improved diagnostic indices compared to either variable considered alone.
CONCLUSIONS: Cervical length and gestational age at admission can be used as a non-invasive method to assess the risk of intra-amniotic inflammation in preterm labor and intact membranes.