Endocrine Abstracts

Objectives: Hyperthyroidism in pregnant women is a clinical concern, and it is important to surveil any change in the occurrence of hyperthyroidism within the pregnant population specifically, especially when a mandatory iodine fortification (IF) program is implemented as it was in Denmark in the year 2000. This longitudinal study aimed to investigate any change in the use of antithyroid drugs (ATD) for the treatment of hyperthyroidism in Danish pregnant women during a 20-year period before and after the implementation of IF.

Methods: We performed a nationwide register-based study of all singleton liveborn pregnancies in Denmark from 1997-2016 (n =1,191,904). Before the implementation of mandatory IF, regional differences in iodine status were seen with moderate iodine deficiency in west and mild iodine deficiency in east Denmark (divided by the Great Belt). Information on maternal use of ATD in pregnancy was obtained from registrations of redeemed prescriptions of drugs and linked to information in the Medical Birth Register. Longitudinal changes regarding ATD use in pregnancy were evaluated as the frequency per 1,000 pregnancies and using logistic regression (adjusted odds ratio (aOR) with 95% confidence interval (CI)) adjusting for potential confounders (e.g. maternal age and smoking).

Results: Before the year 2000, and thereby before the implementation of mandatory IF, the use of ATD in pregnancy was lower in west than in east Denmark (Table). After the year 2000, and thereby after the implementation of mandatory IF, the use of ATD in pregnancy increased overall and in east and west Denmark specifically (Table). The increase reached a similar plateau in both regions and was followed by a decrease towards the end of the 20-year period, which was most pronounced in east Denmark (Table).

Conclusions: The use of ATD for the treatment of hyperthyroidism in pregnancy in Denmark increased in the years following the implementation of mandatory IF and then levelled out. However, baseline values and the observed changes during follow-up differed according to prior population iodine status in each of the regions.