Treating Hypothyroidism and hypothyroxinemia in pregnancy? Clinical dilemma continues.

Treating antenatal patients with levothyroxine who have hypothyroidism or hypothyroxinemia between 8 to 20 weeks of pregnancy did not result in better cognitive outcome and IQ in children through 5 years of age as compared to women who received placebo.

The study was published online on March 2, 2017 in the New England Journal of Medicine.

Earlier studies have shown that the fetus requires thyroxine for normal neurocognitive development specially in first half of pregnancy. Subclinical hypothyroidism is associated with numerous adverse pregnancy outcomes like miscarriage, preterm delivery, low birth weight, and lower-than-normal IQ in offspring.  

The debate to treat subclinical hypothyroidism in pregnancy continues as different societies recommend different guidelines for routine screening of all pregnant women for hypothyroidism. 

ACOG advises against routine screening of all pregnant women for hypothyroidism at this stage because of lack of clear cut benefits in absence of robust clinical trials evidence.

While American Thyroid Association (ATA), advises for treating subclinical hypothyroidism in pregnancy despite lack of clear cut benefits. In fact, ATA recently released new guidelines on thyroid disease in pregnancy. The article can be accessed here.

The current multicenter study by Casey et al. screened all study participants for subclinical hypothyroidism (TSH = 4mIU per liter or more and normal free thyroxine (T4) level (0.86 to 1.90 ng per deciliter) and hypothyroxinemia (normal thyrotropin level (0.08 to 3.99 mU per liter) and a low free T4 level (<0.86 ng per deciliter)

Women in either groups were randomized to receive thyroxine or placebo. Thyroid function was done monthly and the children were followed up for 5 years for cognitive development and IQ tested at 5 years.

There was no significant difference between IQ levels of children in subclinical hypothyroidism (97) and placebo (94) and hypothyroxinemia (94) and placebo (91) at 5 years of age.

No significant differences in maternal pregnancy outcome and neonatal morbidity were observed between the groups.

David Cooper, MD, Johns Hopkins University School of Medicine, Baltimore, Maryland, and Elizabeth Pearce, MD, Boston University School of Medicine, Massachusetts wrote an editorial accompanying the article in which they compared the study findings with several other earlier trials which also failed to show much maternal and neonatal benefits.

They concluded that starting the treatment for subclinical hypothyroidism and hypothyroxinemia is not much beneficial if done well into second trimester, but it is inexpensive and will do no harm. It could be beneficial if the screening and initiation of treatment is done well in first trimester.