Sequential First- and Second-trimester TSH, Free Thyroxine, and Thyroid Antibody Measurements in Women with Known Hypothyroidism: a FaSTER Trial Study

Objective: 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.

Study Design: 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.

Results: 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.

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