In the Journals

High TSH levels after hypothyroidism therapy increase miscarriage risk

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August 20, 2014

Women treated with levothyroxine are likely to have thyroid-stimulating hormone levels above the gestational target, linking them to a higher risk for miscarriage, according to research published in The Journal of Clinical Endocrinology & Metabolism.

Through a historical cohort analysis, researchers in the United Kingdom found thyroid-stimulating hormone (TSH) levels surpassed the 2.5 mU/L recommended during the first trimester, with likelihood of miscarriage increasing at levels exceeding 4.5 mU/L.

“Almost half of women of reproductive age who take levothyroxine for primary hypothyroidism have a thyroid status that is not optimal for pregnancy according to current guidelines,” the researchers wrote. “Furthermore, up to 60% of pregnant women have suboptimal TSH levels in early pregnancy.”

Using the UK General Practice Research Database, Peter N. Taylor, BSc MBChB, MSc, of the Cardiff University School of Medicine and the University of Bristol, and colleagues identified 7,978 women aged 18 to 45 years first prescribed levothyroxine between 2001 and 2009 and 1,013 pregnancies in which therapy was initiated at least 6 months prior to conception.

The investigators measured TSH, miscarriage and delivery status and obstetric outcomes.

TSH levels were >2.5mU/L in 46% of the women treated with levothyroxine. Among pregnant women with TSH measured in the first trimester, 62.8% had levels >2.5 mU/L and 7.4% had levels >10 mU/L.

Women with TSH levels >2.5 mU/L in the first trimester demonstrated an increased risk of miscarriage compared with women with TSH levels between 0.2 mU/L and 2.5 mU/L, with adjustments made for age, year of pregnancy, diabetes and social class (P=.008).

Miscarriage risk rose for women with TSH levels between 4.51 mU/L  and 10 mU/L (OR=1.80; 95% CI, 1.03-3.14) and nearly quadrupled at TSH levels >10 mU/L (OR=3.95; 1.87-8.37). The risk did not increase when TSH levels were between 2.51 mU/L and 4.5 mU/L (OR=1.09; 0.61-1.93).

“There is 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,” the researchers wrote.

Disclosures: The researchers report no relevant disclosures.

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