Do Levothyroxine Adjustments During Pregnancy Differ Between Users of Tablet and Nontablet Formulation? A Real-World Study

Objective: We aimed to assess the levothyroxine (LT4) dosage needed to achieve a target thyrotropin (TSH) ≤2.5 μIU/mL in LT4 tablet and nontablet users during the first half of pregnancy. Methods: We conducted a retrospective analysis on pregnant women with hypothyroidism on LT4 at our university hospital over a period of 4 years. Inclusion criteria were (1) 0.5 μIU/mL < TSH < 4.0 μIU/mL after the first visit; availability of serum TSH every 30 to 40 days until midpregnancy; correct LT4 intake and compliance. Predictors of achieving TSH ≤2.5 μIU/mL were explored using a multivariable probit regression model. P value lower than .05 was considered statistically significant. Results: We included 212 pregnant women (185 with non-post-thyroidectomy hypothyroidism and 27 with post-thyroidectomy hypothyroidism) on LT4 (tablet in 132 women [62.3%], whereas nontablet in 80 women [37.7%]). In non-post-thyroidectomy hypothyroidism, the adjusted analysis, accounting for confounders (ie, maternal weight, thyroid volume, and type of hypothyroidism), revealed that both LT4 dose (P = .001) and formulation (P = .036) were independent and significant predictors of achieving the TSH target. In non-post-thyroidectomy hypothyroidism, the required dose to achieve a 90% probability of success (TSH ≤2.5 μIU/mL) was lower for the nontablet group (1.5 μg/kg/d; 95% CI: 0.47-2.62) than for the tablet group (2.4 μg/kg/d; 95% CI: 1.8-5.6). Conclusion: In pregnant women with non-post-thyroidectomy hypothyroidism lower LT4 dosages may be necessary to achieve TSH between 0.5 μIU/mL < TSH ≤ 2.5 μIU/mL with LT4 nontablet compared with tablet formulations (therapeutic superiority).