FRI484 Assessment Of Early-trimester Maternal Thyroid Function And Iodine Nutritional Status Of Pregnant Women In Northern Taiwan
Authors: Su Guan-Yu , Yeh Chang-Ching , Yang Chen-Chang , Hwu Chii-Min , Chen Harn-Shen , Wang Fan-Fen , Jui Huang Chun 
Published: October 2023

Disclosure: G. Su: None. C. Yeh: None. C. Yang: None. C. Hwu: None. H. Chen: None. F. Wang: None. C. Huang: None.

Background: The American Thyroid Association (ATA) has proposed to lower the early-trimester upper limit of the TSH reference interval to become 0.5 mIU/L less than the non-pregnant value. The local-regional reference intervals in Taiwan is unknown. The aim of the study is to evaluate the early-trimester thyroid function and iodine nutritional status of pregnant women in Taiwan. Methods: Women aged ≥20 years-old and in gestation 8 to 15 weeks were recruited in Taipei Veterans General Hospital from March 2019 to July 2022. Thyroid function and antibodies, including TSH, free T4, free T3, total T4, total T3, anti-thyroglobulin antibody (aTG) and anti-thyroidperoxidase antibody (aTPO), TSH receptor antibody, were measured. The gestation-specific thyroid function reference range was derived from the 2.5th and 97.5th percentiles of the studied women. Random spot urine sample was collected and urinary iodine concentration was checked by inductively coupled plasma mass spectrometry. A simple food frequency questionnaire was also completed. Results: A total of 211 women were enrolled and the derived early-trimester upper limit of serum TSH (median: 0.92 [0.007-3.08] uIU/mL) was lower than the value provided by the manufacturer (0.27-4.2 uIU/mL), while the upper limit of free T4 (median: 1.28 [0.93-2.15] ng/dL) and free T3 (3.00 [2.30-5.10]ng/dL) were both higher than the non-pregnant value (0.93-1.7 ng/dL and 2.0-4.4 ng/dL, respectively). The range of total T4 (median: 9.90 [6.39-15.36] ng/dL) and total T3 (median: 136 [89.50-223.20] ng/dL) in the studied women were similar to the non-pregnant range (5.1-14.1 ng/dL and 80-200 ng/dL, respectively). The positivity rate of aTG & aTPO were 8.6%. Two patients with mild Graves’ disease and three patients with subclinical hypothyroidism were incidentally detected and treated. The positive predictive value for detecting thyroid dysfunction using the non-pregnant reference interval was only 15.9% because subclinical hyperthyroidism (18.2%, n=37) would be over-diagnosed and subclinical hypothyroidism (1.0%, n=2) would be under-diagnosed. The overall median UIC was 160.9 μg/L, indicating a sufficient iodine status. Dairy products were the most commonly consumed iodine-containing food type with 71.8% of the pregnant women ingesting dairy products ≥3 days/week. The median intake frequency for seaweed, fish, and seafood were one day per week. Approximately 34.0% of the women took multivitamin every day, but 58.4% of the women never took multivitamin. Conclusion: Our results indicate that the iodine nutritional status in the early trimester of pregnancy is adequate and that the upper limit of serum TSH was approximately 1.12 uIU/mL lower than the upper limit provided by the manufacturer. Gestation-specific thyroid function reference intervals are needed for correct diagnosis of thyroid dysfunction in pregnancy.

Presentation: Friday, June 16, 2023