What happens to thyroid hormone levels during pregnancy?

During pregnancy, thyroid hormone levels typically increase due to several physiological changes that support the needs of the developing fetus. The increase of approximately 25-30% in levels of thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3), is primarily driven by the rise in human chorionic gonadotropin (hCG) and the increased demand for thyroid hormones to support fetal growth and development.

The placenta also synthesizes hormones that can enhance the production and utilization of thyroid hormones. These increased levels help maintain metabolic homeostasis for both the mother and the fetus and are crucial for normal brain development in the unborn child. Therefore, the correct response reflects this significant boost in thyroid hormone production during pregnancy, which is necessary to accommodate the greater demands placed on the maternal body as well as to ensure optimal fetal health.