Sacral stress fractures are an unusual cause of low-back pain first described by Laurie in 1982. They usually occur in elderly osteoporotic patients (insufficiency fractures). Rarely, they occur in women during the last trimester of pregnancy or in the early postpartum period like in this case. It remains unclear whether this is insufficiency or fatigue fractures. 

Risk factors of sacral stress fractures in women include vaginal delivery of a high-birth-weight infant, increased lumbar lordosis, excessive weight gain and rapid vaginal delivery. Sacral stress fractures are under-diagnosed due to non-specificity of symptoms and low sensitivity of plain radiography.