Endocrine Abstracts

Thyroid disease during pregnancy is associated with adverse pregnancy outcomes and suboptimal fetal development. During the last decades, guidelines for diagnosing thyroid disease during pregnancy have changed considerably, and there has been increased awareness. This study aimed to describe the prevalence of thyroid disease treatment over time among pregnant women in Norway. We combined historical data from the Medical Birth Registry of Norway and the Norwegian Prescription Database, identifying pregnant women using thyroid therapy before, during and after pregnancy from 2004 to 2018. A total of 855.067 pregnancies were included in the analyses. The proportion of women using thyroid hormone replacement therapy during pregnancy increased from 1.46% (n=800) in 2004 to 3.57% (n=1940) in 2018. The proportion of women using antithyroid medications also increased from 0.04% (n=20) in 2004 to 0.10% (n=56). During these 15 years, the mean maternal age increased by 0.9 years. When adjusting for age, the risk for being on thyroid hormone replacement therapy during pregnancy increased by an average of 5% per year (odds ratio 1.05, 95% confidence interval 1.05−1.05). The reasons behind the increased use of thyroid therapy could be many. Firstly, an enhanced focus on better diagnostics lead to an increased prevalence of thyroid disease, which is evident by the results of a repeated population-based cross-sectional study in Norway. However, one of the key clinical issues in this field is the definition of gestational thyroid disease. A second reason could be the increase in inadequate iodine intake among the pregnant population. Recent study from Norway found that pregnant and postpartum women with mild-to moderate iodine deficiency had altered thyroid. Furthermore, experimental and epidemiological studies have shown that a wide spectrum of environmental contaminants have the potential to adversely affect the hypothalamic-pituitary-thyroid axis, resulting in reduced maternal thyroid hormone synthesis affecting fetal neurodevelopment. Another possible contributor to the increased use of thyroid therapy could be that euthyroid women, with thyroid autoantibodies, use thyroid hormone treatment. The proportion of babies born after assisted reproductive therapy has increased by 2.2% during the studied period. During the recent 15 years, there has been a substantial increase in the use of thyroid hormone therapy in Norwegian pregnant women. We speculate that this could be due to an increased awareness in combination with overdiagnosis because of inappropriate diagnostic criteria. To truly understand the possible causes and consequences of this development, further research is warranted.