A new study by Rosa Marie Kiil and team showed that, at 12 months after giving birth, 41% of women satisfied the criteria for current Assessment of SpondyloArthritis international Society (ASAS) sacroiliitis, which might lead to erroneous axial spondyloarthritis (axSpA) assignments in postpartum women with back pain. The findings of this study were published in Arthritis and Rheumatology.
Women may experience sacroiliitis associated with axial spondyloarthritis before or after giving birth, according to sacroiliac joint (SIJ) MRI results. In order to better understand the prevalence, development, and topography of SIJ MRI lesions in pregnant and postpartum women, this study was done.

103 first-time moms who received up to five serial SIJ MRIs during gestational week 20 and 12 months after giving birth were included in this prospective cohort research. Following calibration, three assessors independently assessed structural lesions using the Spondyloarthritis Research Consortium of Canada (SPARCC) and a novel two-plane assessment method, as well as bone marrow edema (BME), including sacroiliitis in accordance with the Assessment of SpondyloArthritis International Society.
The key findings of this study were:
BME was prevalent throughout pregnancy and the postpartum period, culminating at 3 months postpartum with an incidence of 69% (SPARCC)/80% (two-plane), although it was remained prevalent at 12 months postpartum in 54% (SPARCC)/58% (two-plane).
At 12 months postpartum, 41% of women met the criteria for sacroiliitis according to the current ASAS definition, whereas 21%/14% of women matched the criteria for active/structural SIJ lesions according to the newly suggested ASAS MRI thresholds.
At all timepoints, BME tended to concentrate in the anterior middle joint parts, and ligamentous BME was uncommon.
Just 2.8% of women had SPARCC erosion scores below 3 (ASAS threshold) at 12 months postpartum.
In conclusion, it may be possible to distinguish between postpartum strain-related disorders and axSpA-related sacroiliitis using the topographical BME distribution and almost no erosions (ASAS threshold) at 12 months after delivery.
Reference:
Kiil, R. M., Weber, U., Loft, A. G., Maimburg, R. D., & Jurik, A. G. (2023). Evolution of MRI lesions at the sacroiliac joints during and after pregnancy by serial MRI from gestational week 20 to 12 months postpartum. In Arthritis & Rheumatology. Wiley. https://doi.org/10.1002/art.42457