The etiology and underlying mechanisms of pregnancy-associated osteoporosis (PAO) are still unknown, since no systematic analyses exist. Our results indicate that PAO is a heterogeneous, rare but severe disease including a substantial number of fractures with a significant delay from first symptom to diagnose. Pregnancy-associated osteoporosis (PAO) is a rare but severe type of premenopausal osteoporosis. Most common symptom includes acute lower back pain due to vertebral fracture predominantly occurring in the last trimester of pregnancy or immediately postpartum. The exact underlining mechanisms and risk factors of PAO are still unknown, and up to date, there are no published systematic analyses. We identified 102 PAO patients and matched them with 102 healthy controls according to age, region, and gravidity to evaluate risk factors in a large and homogenous population of women. The baseline characteristics and anthropometric data of the two study groups were similar. Eighty-eight percent of the patients with PAO suffered from one or more fractures with a mean of 3.3 fractures per patient. The most common fracture site was the thoracolumbar spine, whereas 29, 37, 48, and 35% of the patients reported fractures at TH11, TH12, L1, and L2, respectively. PAO patients suffered more frequently from excessive dental problems in childhood (p < 0.001). The control group performed significantly more frequently sports both before (p < 0.002) and after puberty (p < 0.01). Compared to the controls, the patients with PAO reported twice as often severe diseases during pregnancy (p < 0.029). Hereby, the frequency of immobilization was twice as often in the PAO group compared to that in the control group (p < 0.005). Our results indicate that PAO is a heterogeneous, rare but severe disease including a substantial number of fractures with a significant delay from first symptom to diagnose. Increased awareness is warranted to immediately start effective treatment.