Trimester-specific reference ranges for thyroid function tests during pregnancy in Iranian pregnant women
Trimester-specific reference ranges for thyroid function tests during pregnancy in Iranian pregnant women
Sima Nazarpour, Fahimeh Ramezani Tehrani, Masoumeh Simbar, Sonia Minooee, Maryam Rahmati , Fereidoun Azizi
Reproductive Endocrinology Research Center
Research Institute for Endocrine Sciences
Shahid Beheshti University of Medical Sciences
Introduction
- Thyroid dysfunction is the second most frequent endocrine disorder in reproductive-aged women.
- Poorly controlled pre-existing thyroid disorders in pregnant women may result in adverse outcomes.
- Physiological changes during pregnancy are associated with alterations in thyroid function which require different biochemical interpretation from that of non-pregnant women and necessitate established pregnancy-specific reference ranges.
- During pregnancy, levels of thyroid hormones (T4 and T3) and thyroxine-binding globulin (TBG) increase, levels of free hormones decline and serum thyrotropin (TSH) concentrations decrease transiently in the first trimester.
- Due to the fluctuations of thyroid hormones both during pregnancy and throughout trimesters, having a gestational-specific and, in particular, a trimester-specific reference range is prerequisite.
- However, their universal adoption among different populations should be cautiously done, due to the differences in ethnicity, iodine-intake adequacy, presence of thyroid autoimmunity, laboratory kits, methods, sample size and the statistical methods applied.
- Also, the cross-sectional nature of some studies might subject their results to inter-individual variations and subsequently, the larger degree of hormonal dispersion.
