Reference intervals in thyroid function tests in the third trimester in pregnant Filipino women

ABSTRACT

BACKGROUND: Pregnancy has been associated with differences in thyroid function.1 Maternal thyroid dysfunction has been shown to be associated with fetal and obstetric complications and prompt management is of importance. It has thus been recommended by the British and American Thyroid Association11,12 that trimester-specific thyroid function test reference ranges be used in the assessment of thyroid dysfunction. Normative values across the trimesters of pregnancy have been conducted in several countries13,17,19 and in the Philippines. Reference rangesin the first and second trimesters of pregnancy were conducted by Patal and Hamin et al. which showed values of TSH 0.14-3.84 uIU/mL, FT4 10.44-21.58 pmol/L, FT3 2.4-5.82 pmol/L in the first trimester and TSH 0.10-4.30 uIU/mL, FT4 9.10-19.40 pmol/L, FT3 2.70- 5.190 pmol/L in the second trimester, respectively.OBJECTIVE: To establish third trimester reference intervals for free thyroid hormones (free triiodothyronine [FT3], free thyroxine [FT4]) and thyrotropin [TSH] from thyroid peroxidase antibody [TPOAb]-negative Filipinopregnant women.DESIGN: This is a prospective, cross-sectional study which included consecutive 200 healthy third-trimester pregnant Filipino women attending Philippine General Hospital (PGH) out-patient services. Serum TSH, FT4, FT3, and TPOAb were measured.MAIN OUTCOME MEASURES: Reference intervals are based on 2.5th and 97.5th percentiles for TSH, FT4, and FT3 among TPOAb-negative third-trimester pregnant Filipino patients.ANALYSIS: All numerical data were entered in MS Excel and analyzed using STATA 12. FT3, FT4 and TSH were expressed as mean ±SD, range at 2.5th to 97.5th percentiles.RESULTS: The reference ranges for TSH, FT4 and FT3 in TPOAb-negative third-trimester pregnant population are as follows: TSH= 0.2-3.0 uIU/mL; FT4 = 9.16-18.64 pmol/L and FT3= 2.09-3.7 pmol/L.CONCLUSION: Reference ranges for thyroid function tests for the third trimester of TPOAb-negative pregnant Filipino women were determined in this study and are as follows: TSH= 0.2-3.0uIU/mL; FT4 = 9.16-18.64pmol/L and FT3= 2.09-3.7pmol/L.