Obstructed labor occurs when the fetus cannot progress through the birth canal despite strong uterine contractions. The most common cause is cephalopelvic disproportion (CPD), where the fetal head is too large to pass through the maternal pelvis. This mechanical mismatch leads to prolonged labor and increases the risk of maternal and fetal complications, often necessitating surgical intervention such as cesarean section. Recognizing CPD early is crucial to avoid labor obstruction and its sequelae.

Reference: Williams Obstetrics, Cunningham et al., 25th Edition.