LAKE BUENA VISTA, FLA. – Levothyroxine therapy during pregnancy in women with subclinical hypothyroidism was associated with a decrease in low birth weight and low Apgar scores but not with a significant decrease in pregnancy loss in a large retrospective cohort study.
In 79 pregnant women with subclinical hypothyroidism (SCH) who received therapy with levothyroxine (LT4), and 285 with SCH who did not receive LT4 therapy, the frequency of low birth weight (less than 2,500 g) was 1.3% vs. 10%, respectively, and the frequency of Apgar scores of 7 or less at 5 minutes was 0% vs. 6.9%, Dr. S. Maraka reported at the International Thyroid Congress.
The rate of pregnancy loss was clinically, but not significantly, lower in the treated group (5.1% vs. 8.8%), and there was no difference between the groups with respect to 11 other maternal and neonatal outcomes, Dr. Maraka of the Mayo Clinic, Rochester, Minn., said at the meeting held by the American Thyroid Association, Asia-Oceania Thyroid Association, European Thyroid Association, and Latin American Thyroid Society.
Study subjects were women evaluated at the Mayo Clinic, Rochester, between January 2011 and December 2013, who had SCH during pregnancy. SCH was defined as thyroid stimulating hormone levels greater than 2.5 mIU/L during the first trimester, or greater than 3 mIU/L but no more than 10 mIU/L during the second and third trimesters. Those with a twin pregnancy or who used medications that might affect thyroid function were excluded.
The treated and untreated groups were similar with regard to age, history of pregnancy loss, and smoking status, but the treated group had higher body mass index and higher TSH levels, Dr. Maraka noted.
The findings that LT4 may improve pregnancy outcome in women with SCH are important because SCH has been associated with an increased risk of adverse pregnancy outcomes in some studies and it has been unclear whether LT4 therapy improves outcomes.
However, the association seen in the current study, which involves the largest cohort reporting pregnancy outcomes of women with SCH treated vs. untreated with LT4 therapy, requires confirmation in randomized trials before widespread use of LT4 therapy for SCH can be recommended, she concluded.
Dr. Maraka reported having no disclosures.