Fig. 1

Flowchart of the study population

Of 105,931 women for whom the date of childbirth was defined, 231 parous women who experienced a low-trauma fracture between the ages of 18–47 years were classified into the premenopausal osteoporosis group. Subsequently, 56 women were classified into the PLO group. The control group was created by randomly selecting 500 women without an ICD-10 code for fragility fracture. JMDC, the Japan Medical Data Center; ICD-10, International Classification of Diseases, 10th revision; PLO, pregnancy and lactation-associated osteoporosis