Sequential first- and second-trimester TSH, free thyroxine, and thyroid antibody measurements in women with known hypothyroidism: a FaSTER trial study

The purpose of this study was to examine how closely hypothyroidism management in the general pregnancy population satisfies recently issued guidelines and to determine whether improvements are indicated.

This was an observational study in which women at 5 recruitment centers in the first- and second-trimester evaluation of risk for aneuploidy trial allowed the use of sequentially obtained first- and second-trimester sera for additional research. Three hundred eighty-nine women had hypothyroidism by self-report. Thyroid-related measurements were performed on all samples between July 2004 and May 2005.

Forty-three percent of the thyroid-stimulating hormone (TSH) values are at or above recently recommended guidelines in the first trimester (2.5 mU/L), as opposed to 33% of the values in the second trimester (3.0 mU/L). Twenty percent of the TSH values are at or above a less restrictive 98th percentile of normal in the first trimester, as opposed to 23% of the values in the second trimester. Mean TSH levels are higher in women with antibodies. Free thyroxine values are unremarkable.

Future strategies should focus on more effectively treating women with hypothyroidism who have persistently elevated TSH values.