Is thyroid replacement therapy recommended for a pregnant patient with a decreased Thyroid-Stimulating Hormone (TSH) level from 3.75 to 2.38?

From the Guidelines

Thyroid replacement therapy is not recommended for a pregnant patient with a decreased TSH level from 3.75 to 2.38 mIU/L. This TSH value of 2.38 mIU/L is actually within the normal range for pregnancy, which is typically considered to be 0.1-4.0 mIU/L in the first trimester, with slight variations in the second and third trimesters, as noted in the guidelines for thyroid disease in pregnancy 1. The decrease from 3.75 to 2.38 represents a normal physiological adaptation to pregnancy rather than a pathological condition requiring treatment. During pregnancy, there are natural changes in thyroid function due to increased metabolic demands, elevated estrogen levels, and the effects of human chorionic gonadotropin (hCG), which has mild thyroid-stimulating properties. These changes typically cause a slight decrease in TSH levels, especially in the first trimester. Initiating thyroid replacement therapy when TSH is in the normal range could potentially lead to iatrogenic hyperthyroidism, which carries risks for both mother and fetus including increased heart rate, anxiety, weight loss, and potential developmental issues for the baby.

Some key points to consider in the management of thyroid function during pregnancy include:

• Regular monitoring of thyroid function throughout pregnancy is recommended, with TSH checks approximately every 4-6 weeks, as thyroid requirements may change as pregnancy progresses 1.
• Women with hypothyroidism should be treated with levothyroxine in a sufficient dosage to return the TSH level to normal, and the dosage should be adjusted every four weeks until the TSH level is stable 1.
• Routine screening for subclinical hypothyroidism is not recommended; however, women with risk factors and symptoms of thyroid diseases should be screened, and subclinical hypothyroidism should be treated 1.
• It is essential to monitor women on thyroid replacement therapy and educate them about its impact on pregnancy, as thyroid replacement dosages typically need to be increased by four to six weeks’ gestation, possibly by 30% or more 1.

Given the current evidence and guidelines, the patient's TSH level of 2.38 mIU/L does not necessitate the initiation of thyroid replacement therapy, and instead, regular monitoring of thyroid function should be continued to ensure that any changes in thyroid status are promptly identified and addressed 1.

From the FDA Drug Label

For pregnant patients with pre-existing hypothyroidism, measure serum TSH and free-T4 as soon as pregnancy is confirmed and, at minimum, during each trimester of pregnancy. In pregnant patients with primary hypothyroidism, maintain serum TSH in the trimester-specific reference range The general aim of therapy is to normalize the serum TSH level

The patient's TSH level has decreased from 3.75 to 2.38, which is still within the normal range for the first trimester of pregnancy (although the exact trimester-specific reference range is not provided in the label).

• Monitoring is recommended to ensure the TSH level remains within the normal range.
• There is no indication to start the patient on thyroid replacement therapy at this time, as the TSH level is within the normal range. 2

From the Research

Thyroid Replacement Therapy in Pregnancy

• The patient's TSH level has decreased from 3.75 to 2.38, which is still within the normal range for a pregnant woman 3, 4.
• According to the study by the Italian Association of Clinical Endocrinologists, TSH should be maintained between 1.0 and 3.0 mIU/L in young subjects, including pregnant women 4.
• The American Association of Clinical Endocrinologists recommends that thyroid-stimulating hormone (TSH) should be maintained at the upper normal limit in elderly or fragile patients, but this does not apply to the patient in question 4.
• There is no evidence to suggest that the patient requires thyroid replacement therapy at this time, as her TSH level is within the normal range 3, 4, 5, 6.

Monitoring TSH Levels

• The study published in Endocrine regulations suggests that patients with subclinical hypothyroidism should be monitored for changes in thyroid status, and treatment should only be initiated if the TSH level exceeds 7.0-10 mIU/L 5.
• The Journal of Internal Medicine recommends that the diagnosis of subclinical hypothyroidism should be confirmed by repeat thyroid function tests ideally obtained at least 2 months later, as 62% of elevated TSH levels may revert to normal spontaneously 6.
• Therefore, it is recommended to continue monitoring the patient's TSH levels rather than starting her on thyroid replacement therapy at this time 3, 4, 5, 6.

Treatment Considerations

• Levothyroxine replacement therapy is the first choice for treating hypothyroidism, and the goal of treatment is to achieve a normal TSH level and relieve symptoms 3, 4.
• However, treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L, and overzealous treatment of symptomatic patients with subclinical hypothyroidism may contribute to dissatisfaction among hypothyroidism patients 6.
• In this case, the patient's TSH level is within the normal range, and treatment is not recommended at this time 3, 4, 5, 6.