Which clinical sign indicates obstructed labor?

Bandl's ring is a pathological constriction ring formed between the upper, thickened contractile segment and the lower, overstretched uterine segment during prolonged and obstructed labor. It is a key clinical sign indicating obstructed labor because it reflects the failure of the fetus to descend despite strong uterine contractions. Recognition of Bandl's ring is crucial as it signals imminent risk of uterine rupture, necessitating urgent surgical intervention, typically cesarean section, to prevent maternal and fetal morbidity. Thus, Bandl's ring directly correlates with obstruction in labor progression.

Reference: Williams Obstetrics, Cunningham F.G., 25th Edition.