Osteogenesis imperfecta (OI) is a rare inherited connective tissue disorder with considerable clinical and genetic heterogeneity. The clinical hallmark of OI is liability to fractures due to reduced bone strength. Pregnancy and lactation are periods of increased calcium demand resulting in a decrease in maternal bone mineral density (BMD). This self-controlled case series evaluates fracture risk 12- and 19-months prior to conception compared to a period of 12- and 19 months following childbirth in women with OI. This study is based on data from the Danish National Patient Register collected between 1995 and 2018. Modified Poisson models were fitted to estimate Incidence Rate Ratio in the post/pre-pregnancy period/s, adjusted by parity and age.

The 12-month observation group included 111 women with 205 pregnancies, and the 19-month observation 108 women with 197 pregnancies. We calculated fracture rates (IR) of 48.78 [95%CI 18.55–79.01] per 1000 person years 12 months prior to conception, and of 27.87 [95%CI 10.60–45.14] in the 12 months post-delivery. Comparing pre- and post-pregnancy period we found an incidence rate ratio (IRR) of 1.00 [95%CI 0.42–2.40]. When adjusting for parity and age at delivery no significant change in the IRR was noted. In the 19 months observation-period, the IR per 1000 person years prior to conception was 74.84 [95%CI 44.25–105.43] and the IR postpartum was 36.86 [95%CI 17.55–56.17], leading to an IRR of 0.61 [95%CI 0.31–1.18]. We could not identify any increased risk of fractures when comparing fracture rates during pregnancy and 12 or 19 months postpartum to fracture rates 12 or 19 months prior to conception.