Testing for and then treating pregnant women with mild or “subclinical” underactive thyroid did not improve pregnancy outcomes, newborn baby outcomes, or the child’s IQ at three to five years.
A clearly underactive thyroid (clinical hypothyroidism) in pregnancy has been linked with various adverse outcomes for the mother and baby, including pre-eclampsia, preterm birth, congenital defects and neurodevelopmental delay. This needs treatment. However, there has been debate around the harms and benefits from treating only mildly abnormal blood test results in women who do not show signs of thyroid problems, subclinical hypothyroidism.
These two linked trials randomised 1,203 women with borderline abnormal levels of thyroid-related hormones (but not “clinical” or “overt” hypothyroidism) to receive thyroid replacement treatment, with levothyroxine, or placebo. Treatment had no benefits for mother or baby, including the main outcome of child IQ by three to five years of age.
This supports current UK practice, which does not routinely screen all pregnant women for subclinical thyroid dysfunction.
Read the full document here