The Evolutionary Origins of Obstructed Labor: Bipedalism, Encephalization, and the Human Obstetric Dilemma

Obstructed labor is a common complication of human childbirth. In parts of the world where access to emergency obstetric services is limited, obstructed labor is a major cause of maternal mortality. Women who survive the ordeal of prolonged obstructed labor often end up suffering from an obstetric vesicovaginal fistula or another serious birth injury that leaves them crippled for life. Compared with the other higher primates (chimpanzees, bonobos, gorillas, and orangutans), these problems are uniquely human. This article reviews the evolutionary origins of the human obstetric dilemma with special reference to the changes imposed on pelvic architecture by the assumption of upright, bipedal posture and locomotion. The subsequent development of progressively increasing brain size (encephalization) in hominins led to the present human obstetrical conundrum: how to balance the evolutionary advantage of bigger babies with larger brains against the presence of a narrow pelvis that is difficult for a fetus to traverse during labor. Target Audience: Obstetricians & Gynecologists, Family Physicians Learning Objectives: After completion of this article, the reader should be able to recall the slow evolutionary progress and the importance of standing erect, and summarize development of the maternal and fetal brain and their evolutionary changes that occurred to overcome obstructive labor.