(273) Is Hypothyroidism in Pregnancy Overtreated? A Retrospective Cohort Study from Bulgaria

Background: Hypothyroidism is the second most common endocrine disorder in pregnancy. Untreated, or inadequately treated hypothyroidism has been associated with adverse maternal and fetal outcomes. Pregnancy is a state of physiological and adaptive changes which result in complex effects on thyroid function. In turn, these changes make hypothyroidism diagnosis challenging.

Objectives: Given the rising prescription rates of levothyroxine in non-pregnant individuals, our objective was to evaluate the prevalence and trends of levothyroxine replacement therapy among euthyroid pregnant women.

Methods: We conducted a retrospective cohort study using data from 6,237 pregnant women who delivered at the OB/GYN Hospital "Dr. Shterev” in Sofia, Bulgaria, between January 2017 and December 2022. Thyroid function data were available for 1,749 pregnant women meeting inclusion criteria: aged >18 years, with singleton pregnancies, and thyroid hormone level tests conducted no later than mid-second trimester.

Results: Participants' ages ranged from 20 to 45 years, with a mean of 32.2 ± 4.6 years. According to pregnancy-specific thyroid disorder diagnostic criteria, patients were categorized into euthyroid (n=1069), subclinical hypothyroidism (n=421), hypothyroidism (n=48), isolated maternal hypothyroxinemia (n=160), gestational thyrotoxicosis (n=46), and Graves' disease (n=5). Analysis revealed that 38% (n=404) of euthyroid pregnant women were prescribed levothyroxine. Notably, 77 euthyroid women received hormone replacement therapy due to autoimmune thyroiditis.

Conclusions: Our findings prompt consideration regarding the appropriateness of levothyroxine therapy for euthyroid pregnant women. Clear guidance is warranted on the initiation of hormone replacement therapy during pregnancy.