A Randomized Placebo-Controlled Trial of Thyroxine Therapy for Subclinical Hypothyroidism or Hypothyroxinemia Diagnosed During Pregnancy (HD 34116-11)
This study consists of two strata, each of which is a randomized, double-masked placebo-controlled
clinical trial conducted in parallel. The first stratum will consist of pregnant women diagnosed with
subclinical hypothyroidism, and the second of pregnant women diagnosed with hypothyroxinemia. in
each stratum, 500 hundred women will be randomized to one of two study arms: 1) a daily thyroxine
supplement in capsule form or 2) matching placebo.
The starting dose of thyroxine for the subclinical hypothyroidism stratum is 100 mcg. Subsequent doses
will be adjusted in 25 mcg increments based on the patient's TSH level, which will be assessed monthly
in a blinded fashion. The starting dose for the hypothyroxinemia stratum is 50 mcg. Subsequent doses
will be adjusted in 25 mcg increments based on the patient's free-T4 level, which also will be assessed
monthly in a blinded fashion.
a. Subclinical hypothyroidism as defined by an elevated TSH (>= 4.00 mU/L) and a free-T4 in the normal range (i.e. 0.86 to 1.90 ng/dL)
b. Hypothyroxinemia as defined by a TSH in the normal range (0.08 to 3.99 mU/L) and a low
free-T4 (<0.86 ng/dL).
2. Singleton pregnancy
3. Gestational age at randomization no earlier than 8.0 weeks and no later than 20.6 weeks based on clinical information and evaluation of the earliest ultrasound.