ATLANTA – Prenatal treatment of maternal subclinical hypothyroidism or hypothyroxinemia conferred no cognitive, behavioral, or neurodevelopmental benefit to children up to age 5.
The findings of two parallel randomized trials suggest that prenatal screening for these conditions is not necessary, Dr. Brian Casey said at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine. The data also support the American College of Obstetricians and Gynecologists’ 2007 recommendation against routine screening, said Dr. Casey, chief of maternal-fetal medicine and obstetrics at the University of Texas Southwestern Medical Center, Dallas.
Dr. Brian Casey
The issue of whether to treat pregnant women for subclinical hypothyroidism has been debated for years. Studies in the early 2000s suggested that prenatal levothyroxine did improve child neurocognitive outcomes, but more recent studies, including a 2012 randomized trial, do not.
These data have led both the American College of Obstetricians and Gynecologists and the Endocrine Society to recommend against screening for subclinical hypothyroidism in pregnant women.
Dr. Casey and his colleagues conducted two large parallel randomized studies, one in women with subclinical hypothyroidism and another in women with hypothyroxinemia. Subclinical hypothyroidism was defined as a thyroid stimulating hormone (TSH) level of at least 4 mU/L with normal free T4. Hypothyroxinemia was defined as a normal TSH but a free T4 of less than 0.86 ng/dL.
The primary outcome in each group was child IQ at 5 years. Secondary outcomes were scores on neurodevelopmental and behavioral measures, including the presence of attention deficit hyperactivity disorder, conducted at ages 3, 4, and 5 years.
All women in the trials had a singleton pregnancy of less than 20 weeks’ gestation, with no known history of thyroid disease.
The subclinical hypothyroidism group comprised 677 women. They were a mean of 27 years old, with a mean gestational age of 16.5 weeks. Baseline TSH was 4.5 mU/L; baseline free T4 was 1 ng/dL. All had normal urinary iodide. They were randomized to placebo or to daily 100 mcg levothyroxine. The treatment goal was a TSH of 0.1-2.5 mU/L. Most (93%) achieved this by 21 weeks’ gestation.
There was no significant difference in the primary outcome of child IQ at 5 years between the treated and untreated groups (97 vs. 94). On the Bayley Scales of Infant and Toddler Development, scores of cognition, motor skills, and language were similar in each group at both 12 and 24 months. The Differential Ability Scales scores at 3 and 4 years were also similar. The Child Behavior Checklist scores at ages 4 years and 5 years were similar. There was no indication of an increase in ADHD.
The hypothyroxinemia trial comprised 467 women. They were randomized to placebo or to 50 mcg levothyroxine. These women were a mean of 28 years old with a mean gestational age of 18 weeks. Their baseline TSH was 1.5 mU/L, and baseline free T4 was 0.8 ng/dL. All had normal urinary iodide. The treatment goal was a free T4 of between 0.86 and 1.90 ng/dL. Most (83%) achieved this by 23 weeks’ gestation.
There was no difference on the primary outcome of child IQ at 5 years (94 vs. 91). On the Bayley Scales of Infant and Toddler Development, scores of cognition, motor skills, and language were similar in each group at both 12 and 24 months. The Differential Ability Scales scores at 3 years and 4 years were also similar. The Child Behavior Checklist scores at ages 4years and 5 years were similar. There was no indication of an increase in ADHD.
Dr. Casey added that there was no interaction between gestational age at baseline and treatment outcomes, suggesting that there may be little foundation to the argument that treating earlier in pregnancy is key.
He had no financial disclosures.