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Published on: June 6, 2014
Interpretation of in-vitro thyroid function tests during pregnancy
British Journal of Obstetrics and Gynaecology
|June 1, 1983
Summary
Interpreting pregnancy thyroid function tests is complex. This study monitored thyroid hormones, finding changes in thyroxine and TBG but stable TSH, providing trimester-specific reference ranges.
Area of Science:
- Endocrinology
- Reproductive Medicine
- Clinical Chemistry
Background:
- Interpreting in-vitro thyroid function tests during pregnancy is challenging due to hormonal fluctuations.
- Oestrogen's effect on thyroid binding globulin (TBG) significantly impacts thyroid hormone measurements.
Purpose of the Study:
- To clarify thyroid hormone interpretation during pregnancy.
- To establish trimester-specific reference ranges for key thyroid hormones.
Main Methods:
- Serum concentrations of total thyroxine (T4), free T4, TBG, T4/TBG ratio, tri-iodothyronine (T3), and TSH were measured.
- Hormone levels were assessed throughout pregnancy, with specific attention to changes by 20 weeks and across trimesters.
Main Results:
- Total T4 and TBG concentrations increased above non-pregnant ranges by 20 weeks.
- The T4/TBG ratio decreased to hypothyroid levels by 20 weeks.
- Free T4 levels were lower in the third trimester, though few subjects exhibited hypothyroid values; TSH remained stable throughout pregnancy.
Conclusions:
- Pregnancy significantly alters thyroid hormone levels, necessitating trimester-specific interpretation.
- Established reference ranges are crucial for accurate diagnosis and management of thyroid function during gestation.
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