Thyroid function parameters in normal pregnancies in an iodine sufficient population.

Area of Science:

• Endocrinology
• Obstetrics
• Reproductive Health

Background:

• Thyroid function during pregnancy is crucial for maternal and fetal well-being.
• Understanding normal thyroid hormone levels is essential for accurate diagnosis and management.
• Previous research has not comprehensively described thyroid function parameters throughout normal gestation.

Purpose of the Study:

• To describe thyroid function parameters, including free triiodothyronine (fT3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH), during normal pregnancies.
• To establish trimester-specific reference ranges for these thyroid hormones.
• To determine the applicability of existing TSH reference ranges in pregnant populations.

Main Methods:

• Retrospective observational study utilizing data from 2006-2007.
• Inclusion criteria: women with normal births recorded in the Tyrol birth registry.
• Thyroid function parameters (fT3, fT4, TSH) measured using established methods at the University Hospital in Innsbruck, Austria.

Main Results:

• fT3 and fT4 levels showed normal distribution across trimesters, with slight decreases observed as pregnancy progressed.
• Mean fT3 values ranged from 4.93 ± 0.59 pmol/l in the first trimester to 4.27 ± 0.45 pmol/l in the third.
• Mean fT4 values ranged from 15.23 ± 2.43 pmol/l in the first trimester to 13.32 ± 2.01 pmol/l in the third.
• TSH values exhibited a left-skewed distribution; mean values (after log transformation) ranged from 1.46 ± 1.29 mIU/l to 1.70 ± 2.22 mIU/l across trimesters.

Conclusions:

• Thyroid function parameters in normal pregnancies within an iodine-sufficient population do not significantly differ from non-pregnant individuals.
• The established TSH reference range of 0.3 to 3.5 mIU/l is confirmed as valid for normal pregnancies.
• These findings contribute to research on the association between maternal thyroid function and child cognitive development.