Intrapartum sonography for fetal head asynclitism and transverse position: sonographic signs and comparison of diagnostic performance between transvaginal and digital examination.

Objective: The primary goal of this study was to determine the ultrasonographic signs of asynclitic and transverse head positioning. In addition, we compared the performance of intrapartum ultrasound to vaginal digital examination.

Material & Methods: 150 women were evaluated by 2D transabdominal and translabial ultrasound (US) to detect the asynclitic and deep transverse positions. Transvaginal sterile digital examinations were performed immediately after each intrapartum US assessments, the examinations were repeated at intervals of 45-90 minutes. Examiners were blinded to each other's findings (clinical or sonographic). Data were reviewed and analyzed by an independent reviewer.

Results: The efficacy of digital examination was significantly lower than US evaluation for the detection of either transverse position or asynclitism. The most frequent transverse position was the left one, while the most frequent asynclitism was the anterior one.

Conclusions: Digital pelvic examination for detection of fetal head transverse position during labor is inferior to US, especially in the deep transverse positioning, where caput succedaneum occurs and reduces the diagnostic accuracy of vaginal digital examination. The US examination leads to early detection of persistent transverse position allowing for earlier timing and optimal technique for the operative vaginal delivery. We describe two signs for diagnosing asynclitism. The "squint sign" and the "sunset of thalamus and cerebellum signs" are two simple US signs allowing detection of anterior and posterior asynclitism.