The purpose of this study is to characterize the MRI changes of the sacroiliac joints (SIJs) during pregnancy and following labor and to correlate them with clinical symptoms. Ninety-three pelvic and hip MRIs of pregnant and ≤6 months postpartum women were retrospectively evaluated (Berlin method), for the presence of acute and structural SIJ changes. A telephone questionnaire focusing on pain characterization, co-morbidities, and clinical outcome was conducted with 52 subjects. Findings were correlated with pregnancy week/postpartum time and clinical parameters. SIJ-bone marrow edema (BME) and subchondral sclerosis were a prevalent peripartum finding (46/26 % subjects, respectively), and their frequency increased with pregnancy age. Also, BME, joint fluid, capsulitis, and enthesitis total score were correlated with pregnancy age/postpartum time (r = 0.2-0.31, P = 0.013-0.036). Significant correlation was noted between BME and subchondral sclerosis scores (r = 0.485, P < 0.0001). A sizable proportion of women showed diffuse SIJ BME (7.6 %) and this correlated with slower resolution of symptoms. Indeed, in half of the cases in which MRI was performed due to pregnancy-induced low-back pain (LBP) and diffuse BME was found-spondyloarthropathy ensued. In conclusion, pregnancy and puerperium are associated with a host of acute findings in and around the SIJ, including BME, capsulitis, and enthesitis, reflecting most probably, mechanical load and hormonal changes. While the vast majority of symptoms abate within weeks to several months postpartum, 3.8 % of women go on to develop spondyloarthropathy. Diffuse SIJ BME and the presence of risk factors for spondyloarthropathy are predictive of a chronic course.