Determination of reference intervals of thyroid markers during pregnancy in Urban area of District Rawalpindi Pakistan.

OBJECTIVE: To determine the reference values for thyroid stimulating hormone, free tetra-iodothyronine and total tri-iodothyronine for healthy pregnant women.

METHODS: This cross sectional study was conducted at the Armed Forces Institute of Pathology, Rawalpindi, Pakistan, from January 2016 to June 2017. Pregnant women with normal, single intrauterine, uncomplicated pregnancy were recruited from the local population. Blood sample was taken to analyse thyroid stimulating hormone, free tetra-iodothyronine and total tri-iodothyronine using chemiluminescence immunoassay. For thyroid hormone levels during each trimester 5th and 95th percentiles were calculated as reference intervals. Data was analysed using SPSS 24.

RESULTS: Out of 384 subjects, 188(48.95%) were in their first trimester and 196(51.04 %) females were in their second trimester. There were 109(57.97%) primigravida in the first trimester and 137(69.9%) in the second trimester. Mean age of subjects presenting in the first and second trimester was 25.37±3.78 years and 26.54±4.65 years respectively. Reference intervals for those in the first trimester for thyroid stimulating hormone was 0.05-2.8uIU/ml, for free tetra-iodothyronine14.4-22.7pmol/l and total tri-iodothyronine1.5-3.3nmol/l. For those in second trimester the corresponding values were 0.16-3.3 uIU/ml, 14.2-24.6.0 pmol/l and 1.6-3.1nmol/l.

CONCLUSIONS: Laboratories should adopt trimester-specific reference intervals for thyroid function tests in pregnancy..