From the Research
Normal TSH levels in pregnancy are typically considered to be between 0.09-3.16 mIU/L in the first trimester, 0.25-3.55 mIU/L in the second trimester, and 0.42-3.93 mIU/L in the third trimester, as established by recent studies using real-life clinical data 1. These reference ranges are important because the placenta produces human chorionic gonadotropin (hCG), which has a mild stimulatory effect on the thyroid gland, naturally suppressing TSH levels. Proper thyroid function during pregnancy is crucial for fetal brain development and preventing complications like miscarriage, preterm birth, and preeclampsia. Some key points to consider include:
- The American Thyroid Association (ATA) has provided guidelines for TSH cutoffs in pregnancy, but these have been subject to controversy and revision 2.
- The Endocrine Society has also published clinical practice guidelines for the management of thyroid disease during pregnancy, including recommendations for TSH cutoffs and treatment of hypothyroidism and hyperthyroidism 3.
- Other studies have reported varying reference ranges for TSH in pregnancy, highlighting the need for population-specific and method-specific reference ranges 4, 5. However, the most recent and highest quality study, published in 2021, provides the most accurate and reliable reference ranges for TSH in pregnancy 1. If thyroid dysfunction is detected, treatment is typically with levothyroxine for hypothyroidism, starting at 1-2 mcg/kg/day and adjusting based on TSH levels monitored every 4-6 weeks. Pregnant women with pre-existing thyroid conditions often need dose adjustments as pregnancy progresses due to increased metabolic demands. It is essential to use the most recent and reliable reference ranges for TSH in pregnancy to ensure accurate diagnosis and treatment of thyroid dysfunction, and to minimize the risk of misclassification and adverse pregnancy outcomes.