Randomized Trial Comparing Two Algorithms for Levothyroxine Dose Adjustment in Pregnant Women With Primary Hypothyroidism

Context: Regulation of maternal thyroid hormones during pregnancy is crucial for optimal maternal and fetal outcomes. There are no specific guidelines addressing maternal levothyroxine (LT4) dose adjustments throughout pregnancy. Objective: To compare two LT4 dose-adjustment algorithms in hypothyroid pregnant women. Design: Thirty-three women on stable LT4 doses were recruited at,10 weeks gestation during 38 pregnancies and randomized to one of two dose-adjustment groups. Group 1 (G1) used an empiric two-pill/week dose increase followed by subsequent pill-per-week dose adjustments. In group 2 (G2), LT4 dose was adjusted in an ongoing approach in micrograms per day based on current thyroid stimulating hormone (TSH) level and LT4 dose. TSH was monitored every 2 weeks in trimesters 1 and 2 and every 4 weeks in trimester 3. Setting: Academic endocrinology clinics in Washington, DC. Main Outcome Measure: Proportion of TSH values within trimester-specific goal ranges. Results: Mean gestational age at study entry was 6.462.1 weeks. Seventy-five percent of TSH values were within trimester-specific goal ranges in G1 compared with 81% in G2 (P = 0.09). Similar numbers of LT4 dose adjustments per pregnancy were required in both groups (G1, 3.1+/-2.0 vs G2, 4.163.2; P = 0.27). Women in G1 were more likely to have suppressed TSH, 0.1 mIU/L in trimester 1 (P = 0.01). Etiology of hypothyroidism, but not thyroid antibody status, was associated with proportion of goal TSH values. Conclusions: We compared two options for LT4 dose adjustment and showed that an ongoing adjustment approach is as effective as empiric dose increase for maintaining goal TSH in hypothyroid women during pregnancy.