Endocrine Abstracts

Objectives: Measurement of TSH-receptor antibodies (TRAb) in hyperthyroid, pregnant women is an important tool when distinguishing between the autoimmune Graves’ disease and the physiological gestational hyperthyroidism. Evidence to support a cut-off for TRAb in early pregnancy is needed along with information on the frequency and follow-up of TRAb-positive as opposed to TRAb-negative hyperthyroidism.

Methods: Within the North Denmark Region Pregnancy Cohort (2011-2015), TRAb was measured (BRAHMS TRAK Human, Kryptor Compact, Thermofisher Diagnostics Aps) in stored blood samples from the early pregnancy among all women with low TSH (<0.1 mIU/l) (n=443) and among randomly selected women (n=606). Method- and pregnancy-specific cut-off (95-percentile) for TRAb was established using Regression on Order Statistics. Each woman was followed in the years after the pregnancy for later diagnosis and treatment of thyroid disease (median follow-up: 8.1 years, range: 4-10 years) using Danish nationwide registers. Comparison of groups was performed using Mann-Whitney U Test or Fisher’s exact test as appropriate. Thermofisher Diagnostics Aps supported the biochemical measurements of TRAb.

Results: The established cut-off for TRAb was 1.0 IU/l. Altogether 28 (4.6%) of randomly selected women and 29 (6.5%) of women with low TSH were TRAb-positive. Considering women with low TSH (Table), TRAb-positive women had lower TSH, higher free T4, and lower β-hCG, and they less often terminated the pregnancy with live birth. Among women with low TSH and no known thyroid disease (n=414), maternal follow-up after the pregnancy showed that diagnosis of thyroid disease was more frequent among TRAb-positive (52.5%) as compared to TRAb-negative women (8.4%).

Conclusions: In a large cohort of Danish pregnant women, most women with low TSH in early pregnancy were TRAb-negative and rarely later diagnosed with thyroid disease. The results warrant further studies on TRAb in early pregnancy to substantiate a pregnancy-specific cut-off and to extend the findings on prevalence and follow-up.