Trimester specific reference intervals of thyroid function tests among Nigerian pregnant women

Abstract

Background: Thyroid disorders are common among women of childbearing age with associated adverse pregnancy outcomes. A normal pregnancy results in a number of important physiological changes that alter thyroid function with considerable variations per trimester. American Thyroid Association recommended each laboratory to establish its thyroid function tests reference interval for each trimester. Lack of these reference intervals makes management of thyroid disorders during pregnancy difficult. Objective: To establish trimester-specific thyroid function reference values in pregnancy. Method: Three-hundred apparently healthy pregnant women were recruited into the study. Thyroid function tests [TSH, free T4, free T3, Thyroxin Binding Globulin (TBG)] were assayed using ELISA kits. Trimester-specific reference intervals (2.5th and 97.5th centiles) were calculated for 75, 125 and 100 pregnant women in first, second and third trimesters’ respectively using Microsoft Excel software 2007. Results: Mean ages ± Standard deviation was 25.4 ± 5.98 years respectively (p>0.05). First trimester TSH, Free T4 , Free T3 and TBG reference intervals were (0.03 – 2.41) µIU/L, (0. 84 – 2.06) ng/mL, (1.92–3.51) pg/mL, and (11.32 – 43.17) µg/mL respectively. Second trimester reference intervals for TSH, Free T4, Free T3
and TBG were (0.14 – 3.55) µIU/L, (0.76 – 2.08) ng/mL, (1.65 – 3.96) pg/mL, and (14.51–72.86) µg/mL respectively. Third trimester reference intervals for TSH, Free T4 , Free T3 and TBG were (0.21– 3.12) µIU/L, (0.70–1.70) ng/mL, (1.74 -3.65) pg/mL, and (20.33–72.55) µg/mL respectively. Conclusion: Thyroid function Reference intervals established in keeping with international recommendations.