High thyroid-stimulating hormone levels may increase miscarriage risk in pregnant women, study results suggest.
Previous research links thyroid dysfunction with adverse obstetrics outcomes, but little is known about pregnancy outcomes in women on long-term levothyroxine, according to research published in the Journal of Clinical Endocrinology & Metabolism.
Peter N. Taylor, MSc, MRCP, of the Cardiff University School of Medicine in the United Kingdom, and colleagues examined the association between thyroid-stimulating hormone (TSH) levels and pregnancy outcomes in women treated with levothyroxine.
Within a large database of people who initiated levothyroxine treatment from 2001 to 2009 in the U.K., 7,987 of child-bearing age and 1,013 pregnancies in which treatment began at least 6 months prior to conception were identified.
TSH level exceeded 2.5 mU/L — the recommended upper level in the first trimester — in 46% of women of child-bearing age who were treated with levothyroxine. Among those whose TSH was measured during the first trimester, 62.8% had TSH levels exceeding 2.5 mU/L. Further, 7.4% had TSH levels exceeding 10 mU/L.
Miscarriage risk was higher in women with TSH greater than 2.5 mU/L in the first trimester vs. those with TSH ranging from 0.2 mU/L to 2.5 mU/L in the first trimester. Adjustments for age, year of pregnancy, diabetes and social class were made (P=.008).
Miscarriage risk was also higher in women with TSH ranging from 4.51 mU/L to 10 mU/L (OR=1.80; 95% CI, 1.03-3.14) and TSH exceeding 10 mU/L (OR=3.95; 95% CI, 1.87-8.37). Risk for miscarriage, however, was not higher in those with TSH ranging from 2.51 mU/L to 4.5 mU/L (OR=1.09; 95% CI, 0.61-1.93).
“The best pregnancy outcomes were seen in women with target TSH levels, and a strong risk of miscarriage was present at TSH levels exceeding 4.5 mU/L,” the researchers wrote.
“There is therefore a pressing need for better liaison between endocrinologists and primary care practitioners to improve the adequacy of thyroid hormone replacement in pregnancy or preferably before conception.”