Comparison of Transvaginal Sonography in a Recumbent and Standing Position to Predict Spontaneous Preterm Birth

Objective: To evaluate whether longitudinal transvaginal sonography (TVS) in a standing position improves the prediction of spontaneous preterm birth (SPB). Methods: For upright and recumbent posture, the inter- and intra-observer agreement of cervical length (CL) was calculated. In 363 pregnancies at risk for SPB, we determined CL and funnel width (FW), differences between positions and longitudinal measurements from 15 weeks to term. Multivariate logistic regression, ROC analysis and contingency tables were performed in singleton and twin pregnancies. Results: The inter-class correlation coefficient was 0.952 in the recumbent and 0.942 in the upright position and merely influenced by experience. Multiple logistic regression analysis revealed that increasing results of CL and FW in the upright position were positively correlated with either a reduction (long CL) or increase (wide FW) of SPB. The improvement of the prediction of SPB by the diagnostic odds ratio (DOR) in the upright position was evident for FW but not for CL. ROC revealed that FW predicted SPB better in a standing compared to a recumbent position at any gestational age in both singleton and twin pregnancies. Conclusions: TVS in both positions non-invasively reflects the impact of natural postures on the cervical tissue. Recently, it has been shown that funneling is a significant risk factor for adverse perinatal outcome (Rust et al.,AJOG April 2005; 192:1060). The fact that FW occurs earlier in the upright position might help to find proper interventions not only to prevent impending SPB but also to prevent serious neonatal mortality and morbidity.