What happens to a patient's thyroid hormone replacement dose when a woman becomes pregnant?

Rationale: A. Decreasing the dose of levothyroxine during pregnancy would be clinically dangerous and could lead to maternal hypothyroidism. Low maternal thyroid levels are associated with increased risks of miscarriage, preterm birth, and impaired fetal neurological development. The physiological changes of pregnancy necessitate higher hormone levels, making a dose reduction the opposite of what is biologically required. B. Most women require a significant dosage adjustment as soon as pregnancy is confirmed to maintain a euthyroid state. Expecting the pre-pregnancy dose to suffice ignores the increased volume of distribution and the high levels of estrogen that increase thyroid-binding globulin. Regular monitoring of TSH levels is essential every 4 weeks during the first half of pregnancy to ensure adequate replacement. C. The need for increased thyroid hormone is driven by maternal physiological changes and fetal demands that exist regardless of the number of fetuses. While carrying multiples may further stress maternal metabolism, a singleton pregnancy is sufficient to require a dosage increase in nearly 85% of hypothyroid women. The adjustment is a standard requirement for ensuring optimal gestational outcomes for all pregnant women. D. Pregnancy induces a state of increased metabolic demand and elevates thyroid-binding globulin levels, which reduces the amount of free, active thyroid hormone available. Additionally, the fetus relies entirely on maternal thyroid hormone during the first trimester for brain development. Consequently, most women require an increase in their levothyroxine dose by approximately 30% to 50% to maintain target TSH levels.