title: A short cervix in women with preterm labor and intact membranes: a risk factor for microbial invasion of the amniotic cavity.
abstract: OBJECTIVE
  The purpose of this study was to determine whether there was a relationship between sonographic cervical length and the presence of culture-proven microbial invasion of the amniotic cavity in women with preterm labor and intact membranes.
  
  
  METHODS
  Ultrasonography and amniocentesis were performed in 401 patients admitted with preterm labor (22-35 weeks) and cervical dilatation of < or = 3 cm, as assessed by digital examination. Cervical length was determined by transvaginal ultrasound at admission. Outcome variables were the presence of microbial invasion of the amniotic cavity (defined as a positive amniotic fluid culture) and the occurrence of preterm delivery before 35 weeks. Contingency tables, chi2 test, receiver-operator characteristic (ROC) curves, and logistic regression were used for statistical analysis.
  
  
  RESULTS
  The prevalence of microbial invasion of the amniotic cavity was 7% (28/401). Spontaneous preterm delivery (< or = 35 weeks) occurred in 21.4% (82/384) of patients. ROC curve analysis showed a significant relationship between the frequency of microbial invasion of the amniotic cavity and the length of the uterine cervix (area under the curve: 0.77; P < .005). Patients with a cervical length < 15 mm had a higher rate of a positive amniotic fluid culture than patients with a cervical length > or = 15 mm (26.3% [15/57] vs. 3.8% [13/344], respectively; P < .05). Moreover, patients with a short cervix (defined as < 15 mm) were more likely to deliver spontaneously before 35 weeks, 32 weeks, within 7 days, and within 48 hours of admission ( P < .05 for all comparisons). Forty percent of patients (161/401) had a cervical length > or = 30 mm. These patients had a very low risk of microbial invasion of the amniotic cavity (1.9% [3/161]), spontaneous delivery < or = 35 weeks (4.5% [7/154]), < or = 32 weeks (2.6% [2/76]), within 7 days (1.9% [3/154]), and within 48 hours (0% [0/154]) of admission.
  
  
  CONCLUSIONS
  Endovaginal ultrasonographic examination of the uterine cervix in women with preterm labor identifies patients at increased risk for intrauterine infection.
authors.affiliation: Center for Perinatal Diagnosis and Research (CEDIP), Sótero del Río Hospital, P Universidad Católica de Chile, Puente Alto, Chile.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gomez
authors.forename: Roberto
authors.initials: R
authors.lastname: Romero
authors.forename: Jyh Kae
authors.initials: JK
authors.lastname: Nien
authors.forename: Tinnakorn
authors.initials: T
authors.lastname: Chaiworapongsa
authors.forename: Luis
authors.initials: L
authors.lastname: Medina
authors.forename: Yeon Mee
authors.initials: YM
authors.lastname: Kim
authors.forename: Bo Hyun
authors.initials: BH
authors.lastname: Yoon
authors.forename: Mario
authors.initials: M
authors.lastname: Carstens
authors.forename: Jimmy
authors.initials: J
authors.lastname: Espinoza
authors.forename: Jay D
authors.initials: JD
authors.lastname: Iams
authors.forename: Rogelio
authors.initials: R
authors.lastname: Gonzalez
mesh_terms: D000328:Adult; D000649:Amniocentesis; D000653:Amniotic Fluid / Q000382:microbiology; D001424:Bacterial Infections / Q000209:etiology*; D002584:Cervix Uteri / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007752:Obstetric Labor, Premature / Q000209:etiology*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000209:etiology*; D012307:Risk Factors; D014463:Ultrasonography; D014591:Uterine Diseases / Q000209:etiology*