Revisiting the short cervix detected by transvaginal ultrasound in the second trimester: Why cerclage therapy may not help

OBJECTIVE: The purpose of this study was to identify the risk factors that are associated with increased neonatal morbidity in patients who were treat ed for sonographic evidence of internal os dilation and distal cervical sho rtening during the second trimester. STUDY DESIGN: From May 1998 to June 2000 patients between 16 and 24 weeks o f gestation with the following sonographic criteria were randomly assigned to McDonald cerclage or no cerclage: internal os dilation and either membra ne prolapse into the endocervical canal at least 25% of the total cervical length but not beyond the external os or a shortened distal cervix <2.5 cm. Before randomization, all patients were treated identically with an amnioc entesis, multiple urogenital cultures, and therapy with indomethacin and cl indamycin for 48 to 72 hours. Except for the cerclage, all patients were tr eated identically after randomization. Multiple variables of perinatal outc ome were analyzed. A regression model with gestational age at delivery as t he dependent variable was constructed and repeated with neonatal morbidity as the dependent variable. This model was applied to 3 populations: the cer clage group, the no cerclage group, and both groups combined. RESULTS: Of the 135 patients, 20 patients declined randomization, and 2 pat ients were diagnosed with acute chorioamnionitis. Of the 113 patients remai ning, 55 patients were randomly assigned to the cerclage group, and 58 pati ents were randomly assigned to the no cerclage group. There were 8 rescue c erclage procedures (4 in each group). Regression analysis showed that readm ission for preterm labor, chorioamnionitis, and abruption were consistently associated with early gestational age at delivery and increased morbidity. Cerclage did not affect perinatal outcome. CONCLUSION: The sonographic findings of second trimester internal os dilati on, membrane prolapse, and distal cervical shortening likely represent a co mmon pathway of several pathophysiologic processes. Use of cerclage does no t alter any perinatal outcome variables. Increased neonatal morbidity in th ese patients appears to be associated with subclinical infection, preterm l abor, and abruption.