Pregnancy-related hip diseases epidemiology has been poorly evaluated. We report our experience of gestational and postpartum hip diseases and evaluate their incidence.

(1) Prospective survey: all pregnant or early postpartum women suspected to have hip involvement during their follow-up in an Obstetric unit were referred to a rheumatologist. If clinically confirmed, magnetic resonance imaging (MRI) and additional investigations as needed were performed. This survey had 2 years duration. (2) Retrospective study: all cases of definite (with MRI confirmation) pregnancy-related hip disease referred to our Rheumatology unit during the past 15 years were analyzed.

During the 2-year prospective survey, 3 patients (4 hips) of pregnancy-related hip disease were observed over 4900 pregnancies (1 case of transient osteoporosis of the hip (TOH) and 2 cases of occult fracture of the femoral head). During the 15-year retrospective study, 12 patients (17 hips) with hip diseases during pregnancy or early postpartum were identified. There were 6 patients (9 hips) with TOH, 4 patients (6 hips) with occult fracture of the femoral head, 1 patient with osteonecrosis of the femoral head, and 1 coxitis in a patient with ankylosing spondylitis. Differentiating diagnosis between TOH and occult fractures could only be made by MRI. Five of the 6 women with TOH had osteopenia at the lumbar spine at dual energy X-ray absorptiometry (DEXA). The 4 women with occult fractures had either osteopenia or osteoporosis at the lumbar spine.

Hip diseases are infrequent during pregnancy and early postpartum. Transient osteoporosis of the hip and occult stress fractures of the femoral head appear the main causes and those diagnoses justify evaluation for an underlying bone fragility. Osteonecrosis is very rare in this setting.