Which statement about TSH and T4 in early pregnancy is correct?

In early pregnancy, the typical physiological changes in the thyroid hormones and Thyroid-Stimulating Hormone (TSH) levels reflect the body’s adaptation to the developing fetus. During the first trimester, levels of T4 (thyroxine) generally increase due to enhanced production stimulated by the human chorionic gonadotropin (hCG), which shares structural similarities with TSH.

As a result of this increase in T4 production, TSH levels tend to decrease. This occurs because the elevated levels of thyroid hormones provide negative feedback to the pituitary gland, leading to a reduction in TSH secretion. Essentially, the body adjusts to ensure an adequate supply of thyroid hormones for both the mother and the developing fetus, which is crucial for healthy fetal development, particularly for brain development.

This understanding of the hormonal interplay during early pregnancy highlights why the statement indicating that TSH falls and thyroid hormones rise is accurate within this context.