Type 1 diabetes impairs female fertility even before it is diagnosed

Aims The aim of this study was to assess the fertility rate in Taiwanese women before and after a diagnosis of type 1 diabetes. The potential risk factors which may have influenced fertility were also investigated. Methods We conducted this retrospective, nationwide, population-based, matched cohort study using data from the Taiwan National Health Insurance Research Database. The diabetic group (n = 1191) included women with type 1 diabetes aged between 16 and 30 years in 2000. The non-diabetic group (n = 4764) was matched by sex, gender, income, and urbanization. The endpoints, including live births, abortions, and fertility, were tracked until the end of 2013. Poisson regression was used to assess incidence rate ratios (IRRs). We also analyzed the influence of autoimmune thyroid disease, diabetic ketoacidosis, diabetic complications, and daily insulin dose on the endpoints. Results The diabetic group had a lower rate of live births (IRR 0.67 [95% CI 0.62–0.73]) than the non-diabetic group, and it was even lower when combined with hyperthyroidism (IRR 0.54 [0.39–0.74]). There were also fewer live births before a diagnosis of diabetes than after a diagnosis of diabetes (IRR 0.58 [0.52–0.65] vs. 0.80 [0.71–0.90]). Diabetic ketoacidosis and a higher daily insulin dose were strongly associated with abortion. Diabetic complications significantly reduced the number of live births. Conclusions Type 1 diabetes compromises female fertility, even before it is diagnosed. Associated hyperthyroidism further reduces fertility. Blood glucose and thyroid function surveillance in infertile females may allow for an early diagnosis of type 1 diabetes and associated thyroid disease.