Subacute thyroiditis during pregnancy: clinical characteristics of seven cases

Objective: There are few reports of subacute thyroiditis (SAT) during pregnancy. This study aimed to clarify the clinical characteristics of SAT in pregnant patients. Methods and results: Seven patients diagnosed with SAT during pregnancy at our institution from January 2004 to December 2021 were identified, and their clinical findings were retrospectively examined. At SAT diagnosis, the median age was 34 (range: 31–42) years, the median duration of pregnancy was 5 (4–24) weeks, and all patients had neck pain but no fever. On laboratory examination, median (range) free thyroxine, free triiodothyronine, and C-reactive protein levels were 2.66 (1.14–7.77) ng/dL, 7.1 (3.3–16.1) pg/mL, and 2.22 (0.42–5.79) mg/dL, respectively, and all patients had a hypoechoic lesion of the thyroid gland. Three patients (43%) were treated with steroids, and three patients (43%) received replacement therapy with levothyroxine for hypothyroidism following destructive thyroiditis. There were no pregnancy complications in any of the cases. These seven patients (pregnancy group) were compared with 217 non-pregnant female patients (non-pregnancy group) aged 31 to 42 years who were diagnosed with SAT at our institution from 2016 to 2019. The frequency of body temperatures above 37°C was lower in the pregnancy group than in the non-pregnancy group (0% vs 65%). Conclusion: Patients who develop SAT during pregnancy may have less fever than non-pregnant patients with SAT. There were no pregnancy complications in the pregnancy group in this study. This suggests that adverse pregnancy outcomes may be avoided by the appropriate management of SAT, including hypothyroidism after destructive thyroiditis.