According to the current study by Bjelland and colleagues, pelvic girdle pain affects 1 in 5 pregnant women and is a major cause of sick leave during pregnancy. The diagnosis is based on the woman's subjective experience rather than on objective findings. Pelvic girdle pain typically presents in the first half of pregnancy and resolves after delivery. Factors predicting persistent pain include high pain intensity and the number of pain sites, but other factors have not yet been examined. This is a longitudinal cohort study of pregnant women, who were recruited at 17 and 30 weeks' gestation and observed to 6 months after delivery, to examine the natural history of pelvic pain syndrome (PGS) and prognostic factors that determine persistent pain 6 months after delivery.