The Fetal Head-Symphysis Distance in Intrapartum Ultrasound Assessment of the Fetal Head Engagement

The mechanism of labor requires positional changes of the presenting fetal part in the maternal pelvis. One of the cardinal movements of labor is fetal head descent in the birth canal. Fetal head descent leads to its engagement in the birth canal. This is usually defined when the largest fetal head diameter (biparietal diameter) passes through the pelvic inlet [1]. Since this is impossible to diagnose directly, many indirect signs, usually by digital examination, are used as a proxy to engagement. Assessing fetal head descent is of utmost importance in labor