Evolution of MRI lesions at the sacroiliac joints during and after pregnancy by serial MRI from gestational week 20 to 12 months postpartum.

At 12 months postpartum 41% of women met the current ASAS sacroiliitis definition, which may result in false positive assignments of axSpA in postpartum women with back pain. The topographical BME distribution and virtually absent erosions (ASAS threshold) at 12 months postpartum may help discriminate postpartum strain-related conditions from axSpA-related sacroiliitis.