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THYROID AND PREGNANCY
Levothyroxine treatment of subclinical hypothyroidism in pregnancy did not improve brain development testing scores in children up to 2 years of age.
BACKGROUND
Thyroid hormone plays an important role in baby’s development during pregnancy. In particular, brain development is very sensitive to thyroid hormones. Because the baby’s thyroid gland does not start making thyroid hormone until 18-20 weeks of pregnancy, it is especially important for pregnant women to have adequate thyroid hormone available during critical period of development in early pregnancy. Several studies have suggested that low thyroid hormone levels (hypothyroidism) in the mother during pregnancy may cause problems with the baby’s brain development.
Hypothyroidism can be either overt hypothyroidism (high thyroid stimulating hormone (TSH) and low thyroxine (free T4 levels) or subclinical hypothyroidism (a milder form of hypothyroidism with high TSH and normal free T4 levels). Guidelines agree that overt hypothyroidism in pregnancy should be treated with levothyroxine to prevent adverse impact on the health of the mother and the baby’s development. However, it is less clear whether subclinical hypothyroidism in pregnancy should be treated because studies have not yet shown clear benefit in treating with levothyroxine. The researchers of this study aimed to evaluate potential benefit of levothyroxine treatment of overt and subclinical hypothyroidism during pregnancy on the child’s subsequent brain development.
THE FULL ARTICLE TITLE
Zhao Z et al 2023 Impact of levothyroxine therapy for maternal subclinical and overt hypothyroidism on early child neurodevelopment: A prospective cohort study. Clin Endocrinol (Oxf ). Epub 2023 Oct 20. PMID: 37859522
SUMMARY OF THE STUDY
A total of 442 pregnant patients before 16 weeks of singleton pregnancy seen at Fudan University hospital in China between January 1, 2012 and December 31, 2013 participated in the study.
Patients were divided into either overt or subclinical hypothyroidism group based on normal ranges recommend by the 2011 American Thyroid Association guidelines. Decision for treatment with levothyroxine was made by patient’s individual endocrinologists. Children of these women were tested at 1, 3, 6, 12, and 24 months of age using a Gesell Development Diagnosis Scale. The scores were used to compare brain status between children born to mothers with subclinical hypothyroidism (SCH group) and those born to mother with overt hypothyroidism (OH group).
Pregnant patients in SCH group were tested for thyroid levels later than those in OH group on average (13.6 weeks vs. 8 weeks of pregnancy). About two-thirds (61%) of patients in OH group were already diagnosed with hypothyroidism before becoming pregnant. On the other hand, 90% of patients in SCH group were diagnosed during pregnancy. On average, patients in SCH group were started on levothyroxine 2 weeks later than patients in OH group. However, most of patients in both groups were taking levothyroxine by the end of pregnancy (99.4% patients in SCH group and 100% in OH group).
Children in SCH group had lower scores in five areas of tests compared to children in OH group: gross motor and social-emotional responses at 3 months, adaptability at 6 months (average score of 98 vs 103), gross motor skills at 1 year (average score of 102.54 vs 104.64), and language skills at 2 years (average score of 106.2 vs 112.64).
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors concluded that children born to mother with subclinical hypothyroidism had lower scores on brain developmental testing compared to those born to mothers with overt hypothyroidism in the first 2 years of life. This finding may be due to differences in when levothyroxine treatment started. Many of women with overt hypothyroidism were already diagnosed and started on treatment before becoming pregnant while most women with subclinical hypothyroidism were diagnosed during pregnancy. Therefore, the results of this study suggest that early treatment of hypothyroidism in pregnancy is especially important to benefit developing baby’s brain. A larger study with comparison group of children born to mothers without thyroid disease and treatment initiation at earlier in pregnancy would be needed to better understand potential benefit of levothyroxine treatment of subclinical hypothyroidism in pregnancy.
— Sun Y. Lee, MD, MSc
ATA RESOURCES
Thyroid Disease in Pregnancy: https://www.thyroid.org/thyroid-disease-pregnancy/
ABBREVIATIONS & DEFINITIONS
Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.
Subclinical Hypothyroidism: a mild form of hypothyroidism where the only abnormal hormone level is an increased TSH. There is controversy as to whether this should be treated or not.
Overt Hypothyroidism: clear hypothyroidism an increased TSH and a decreased T4 level. All patients with overt hypothyroidism are usually treated with thyroid hormone pills.
TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.
Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.
Levothyroxine (T4): the major hormone produced by the thyroid gland and available in pill form as Synthroid™, Levoxyl™, Tyrosint™ and generic preparations.
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