A short cervix in women with preterm labor and intact membranes: a risk factor for microbial invasion of the amniotic cavity.
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.
Gomez
Ricardo
R
Center for Perinatal Diagnosis and Research (CEDIP), Sótero del Río Hospital, P Universidad Católica de Chile, Puente Alto, Chile.
Romero
Roberto
R
Nien
Jyh Kae
JK
Chaiworapongsa
Tinnakorn
T
Medina
Luis
L
Kim
Yeon Mee
YM
Yoon
Bo Hyun
BH
Carstens
Mario
M
Espinoza
Jimmy
J
Iams
Jay D
JD
Gonzalez
Rogelio
R
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*