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

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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.


To compare two LT4 dose-adjustment algorithms in hypothyroid pregnant women.


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.


Academic endocrinology clinics in Washington, DC.

Main Outcome Measure:

Proportion of TSH values within trimester-specific goal ranges.


Mean gestational age at study entry was 6.4 ± 2.1 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, 4.1 ± 3.2; 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.


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.

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