Trimester-Specific Thyroid Function in Pregnant Women with Different Iodine Statuses

Area of Science:

• Endocrinology
• Reproductive Health
• Nutritional Science

Background:

• Iodine is crucial for thyroid hormone synthesis, essential for maternal and fetal health during pregnancy.
• Pregnancy involves significant physiological changes affecting thyroid function and iodine requirements.
• Understanding trimester-specific thyroid adjustments and the impact of iodine status is vital for optimal pregnancy outcomes.

Purpose of the Study:

• To investigate how thyroid function and thyroid volume change across trimesters of pregnancy.
• To examine the relationship between varying levels of iodine status and these trimester-specific changes.

Main Methods:

• A cross-sectional study involving 2,378 healthy pregnant women across three trimesters.
• Assessment of urinary iodine concentration (UIC) to determine iodine status.
• Measurement of thyroid function (TSH, FT3, FT4) and thyroid volume (Tvol) via blood tests and B-ultrasonography.

Main Results:

• Thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels decreased as pregnancy progressed.
• Thyroid volume (Tvol) significantly increased with advancing pregnancy.
• No significant differences in TSH, FT3, or FT4 were found across different iodine status groups.
• Elevated Tvol was observed in the first and third trimesters for women with high UIC (≥500 μg/L).

Conclusions:

• Pregnancy progression, not iodine status, significantly impacts thyroid hormone levels and thyroid volume.
• While thyroid hormones remain stable across iodine groups, increased thyroid volume in high-iodine groups warrants further investigation.