TSH TestingThyroid-stimulating hormone (TSH), or thyrotropin, is measured in the blood sample. It is a hormone released by the pituitary that regulates thyroid hormone production. TSH secretion is controlled by a feedback system known as the hypothalamic-pituitary-thyroid (HPT) axis. When the levels of thyroid hormones in the bloodstream drop below a certain threshold, the hypothalamus in the brain releases thyrotropin-releasing hormone (TRH), which signals the anterior pituitary gland to produce and release TSH. TSH then travels through the bloodstream to the thyroid gland, where it binds to specific receptors on the surface of thyroid cells, stimulating the production and release of T3 and T4. The release of TSH is tightly regulated by a negative feedback loop, meaning that as the levels of T3 and T4 in the bloodstream increase, they inhibit the production of TSH. Conversely, when T3 and T4 levels are low, TSH production increases, stimulating the thyroid gland to produce more hormones.      According to a 2002 ACOG bulletin on thyroid disease, TSH and FT4 or FTI testing should be performed in pregnant women with suspected hyperthyroidism or hypothyroidism. TSH in PregnancyChanges in thyroid function are primarily regulated by hormones, such as hCG and progesterone. In the early days and weeks of the first trimester, hCG binds to TSH receptors on the thyroid, increasing stimulation and production of thyroid hormones. This increase in thyroid hormone production, up to 25% in the first trimester, causes a decrease in TSH production. In the second trimester, TSH levels stabilize and slightly increase from first-trimester levels. In the late stages of the third trimester, TSH levels may decrease again, as the need for the thyroid hormones increases in preparation for labor and delivery. In the first 24 to 48 hours after giving birth, TSH levels typically drop significantly. This drop is primarily due to the sudden reduction in the high levels of hCG. Levels usually start to return to their prepregnancy baseline within the first week postpartum. High TSH in PregnancyA 2019 case-controlled study found that TSH ranges between 2.5 and 4.87 mIU/L increased the risk of miscarriage. The results were similar after controlling for the confounding factors, thyroid peroxidase antibodies (TPOAb) positivity status, and FT4. A 2019 study on hypothyroidism and birth outcomes found postpartum hemorrhage as the most frequent maternal outcome (38.8%). Emergency cesarean section occurred in 23.4% of cases. The risk was increased with a TSH >2.5 mIU/L. Subclinical hypothyroidism throughout pregnancy is associated with a risk of increased rates of induction, longer first stage of labor, premature rupture of membranes (PROM), “failure to progress,” increased chance of hemorrhage, and increased ICU (intensive care unit) stay. Most Common Causes of High TSH in Pregnancy
Low TSH in PregnancyTrue hyperthyroidism is an uncommon condition that complicates approximately 0.1% to 0.4% of pregnancies. Most Common Causes of Low TSH in Pregnancy
Want to Learn More?Explore my Advanced Maternal Lab Analysis course—MEAC-approved for continuing education. Copyright © 2024 Functional Maternity, all rights reserved. Medical Disclaimer: This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.
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Hi There!I'm Sarah Thompson, the author of Functional Maternity, and the upcoming book Beyond Results - A practitioner's Handbook to Effective Functional Lab Analysis in Pregnancy. Lab Tests
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