The Starting Dosage of Levothyroxine for Hypothyroidism during Pregnancy
10.11106/ijt.2026.19.1.60
- Author:
Hyunju PARK
1
;
Arim CHOI
;
Kyung-Soo KIM
;
Soo-Kyung KIM
;
Yong-Wook CHO
Author Information
1. Department of Internal Medicine, CHA Bundang Medical Center, CHA University School of Medicine, Seongnam, Korea
- Publication Type:ORIGINAL ARTICLES
- From:International Journal of Thyroidology
2026;19(1):60-67
- CountryRepublic of Korea
- Language:English
-
Abstract:
Background:and Objective: Maternal hypothyroidism increases the risk of adverse pregnancy outcomes, making appropriate levothyroxine (LT4) replacement essential. However, the optimal initial LT4 dose for women newly diagnosed with subclinical hypothyroidism (SCH) or overt hypothyroidism (OH) during pregnancy remains unclear.This study evaluated the appropriate starting LT4 dose based on baseline thyroid-stimulating hormone (TSH) and body mass index (BMI).
Materials and Methods:This single-center retrospective cohort study included 126 pregnant women from June 2018 to April 2025. After pregnancy was confirmed, all participants started LT4.Patients were categorized by baseline TSH (2.5-4, 4-10, and ＞10 mIU/L) and BMI (＜23, 23-＜25, and ≥25 kg/m2 ) to determine the appropriate LT4 dose. The treatment goal was a TSH level ＜2.5 mIU/L.
Results:Among the 126 patients, 101 (80.2%) were diagnosed with SCH or OH in the first trimester. The mean baseline TSH was 5.19 mIU/L, and 29.4% had autoimmune thyroiditis. Baseline TSH (r=0.315, p＜0.001) was positively associated with weight-based LT4 dose, whereas body weight (r=−0.304, p＜0.001) and BMI (r=−0.248, p=0.005) were inversely associated. The median weight-based LT4 dose was 0.45 μg/kg/day for TSH 2.5-4.0 mIU/L, 0.71 μg/kg/day for TSH 4.0-10 mIU/L, and 1.34 μg/kg/day for TSH ＞10 mIU/L (p for trend ＜0.001). Patients with TSH ＞10 mIU/L required more time to achieve TSH ＜2.5 mIU/L, and those with BMI ≥25 kg/m2 received lower weight-based LT4 doses.
Conclusion:Initial LT4 dosing should be tailored based on baseline TSH and BMI.
