Abstract: Pregnancy leads to significant physiological changes that require trimester-specific reference intervals for thyroid function tests. Accurate assessment of thyroid function is critical to both maternal and fetal health. However, normative data on thyroid hormones for healthy pregnant women in Bangladesh are currently lacking.
This study aimed to assess the trimester-specific reference ranges for thyroid hormones in normal pregnant women.
Methods: This cross-sectional study was conducted at the Department of Fetomaternal Medicine and Obstetrics and Gynecology outpatient of Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh from September 2022 to October 2023. A total of 360 single-tone pregnant women between 18 and 35 years of age were enrolled purposively. Data were analyzed using SPSS version 27.0.
Results: The study revealed significant fluctuations in TSH levels across pregnancy trimesters (p<0.05). In the first trimester, the mean TSH level was 1.55±0.79 μIU/L, which increased to 1.85±0.93 μIU/L in the second trimester and further to 2.29±0.94 μIU/L in the third trimester. Reference intervals in the first, second, and third trimesters were as follows: TSH (0.1-3.09, 0.2-3.6, and 0.35-4.04 µIU/l), FT4 (10.29-20.05, 9.63-17.99, and 9.6-16.65 pmol/L), and FT3 (1.97-6.32, 2.36-5.87, and 2.52-5.74 pmol/L), respectively.
Conclusion: The reference ranges for thyroid function tests show significant differences between trimesters of pregnancy. The use of trimester-specific thyroid hormone reference intervals is imperative to reduce the risk of misclassification of thyroid dysfunction during pregnancy.
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