Reference intervals in evaluation of maternal thyroid function of Manipuri women

Context: The population of Manipur is of different ethnic background from the rest of the country. Several authors have suggested population/ethnic and laboratory specific reference range of maternal thyroid profile of different trimesters. Aims: To find the reference range of thyroid stimulating hormone (TSH), total thyroxine (TT4) and total tri-iodothyronine (TT3) levels for normal pregnant women of native Manipur descendants. Settings and Design: The cross-sectional study was conducted at a teaching Institute after ethical clearance was obtained. Subjects and Methods: A reference populations of 375 normal pregnant women were established after screening about 600 pregnant women. The study excluded patients with hyperemesis gravid arum, past history or family history of thyroid disorders as well as the connective tissue disorders, WHO grade 1 or 2 goiter, or any medications that alter thyroid functions. The serum levels of TSH, TT4, and TT3 were measured using chemiluminescence assay. Statistical Analysis Used: Data for TT3 and TT4 were expressed as mean ± standard deviation, median and 5-95th percentiles. Results: The mean TSH in the three trimesters was 1.06 + 0.45, 1.23 + 0.30, and 1.25 + 0.36, respectively. The normal reference range thus was different from that of the kit reference range. On comparing to the Indian normative reference for the pregnant women, our results were not similar. However, the values were near similar to that of the American Thyroid Association guidelines. Conclusions: We conclude our study results with a new reference range for the pregnant population in Manipur and also emphasis the use of trimester-specific reference range of thyroid hormone.