From the Guidelines
For TSH above 2.5 mIU/L in the first trimester of pregnancy, treatment with levothyroxine is recommended to normalize thyroid function. This recommendation is based on the possible association between high TSH and either increased fetal wastage or subsequent neuropsychological complications occurring in the offspring due to thyroid insufficiency 1. The goal of treatment is to restore the serum TSH concentration to the reference range, which can be achieved by starting with levothyroxine at a dose of 1-2 mcg/kg/day (typically 50-100 mcg daily) taken on an empty stomach 30-60 minutes before breakfast.
Key Considerations
- The requirement for levothyroxine in treated hypothyroid women frequently increases during pregnancy, so serum TSH concentration should be monitored every 6 to 8 weeks during pregnancy and the levothyroxine dose modified as needed 1.
- Pregnant women often require higher doses of levothyroxine compared to their pre-pregnancy dose due to increased metabolic demands and estrogen-induced increases in thyroid-binding globulin.
- Recheck TSH and free T4 levels every 4-6 weeks during the first half of pregnancy and at least once during the second half to adjust dosing as needed.
- Prompt treatment is important because maternal hypothyroidism, even subclinical, has been associated with adverse pregnancy outcomes including miscarriage, preeclampsia, placental abruption, and impaired fetal neurocognitive development.
Monitoring and Adjustment
- After delivery, the levothyroxine dose can typically be reduced to pre-pregnancy levels, with thyroid function reassessment at 6 weeks postpartum.
- It is essential to note that the risks of appropriately managed levothyroxine therapy in pregnancy are minimal 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 recommended daily dosage of levothyroxine sodium tablets in pregnant patients is described in Table 3. Pre-existing primary hypothyroidism with serum TSH above normal trimester-specific range Pre-pregnancy dosage may increase during pregnancy Increase levothyroxine sodium dosage by 12.5 to 25 mcg per day. Monitor TSH every 4 weeks until a stable dose is reached and serum TSH is within normal trimester-specific range.
The management of elevated Thyroid-Stimulating Hormone (TSH) above 2.5 in the first trimester of pregnancy involves:
- Measuring serum TSH and free-T4 as soon as pregnancy is confirmed
- Maintaining serum TSH in the trimester-specific reference range
- Increasing levothyroxine sodium dosage by 12.5 to 25 mcg per day for pre-existing primary hypothyroidism with serum TSH above normal trimester-specific range
- Monitoring TSH every 4 weeks until a stable dose is reached and serum TSH is within normal trimester-specific range 2
From the Research
Management of Elevated TSH in Pregnancy
The management of elevated Thyroid-Stimulating Hormone (TSH) above 2.5 in the first trimester of pregnancy involves initiating or adjusting levothyroxine (LT4) treatment to achieve a TSH level of ≤2.5 mIU/L. Key considerations include:
- Initiating LT4 treatment with a dose of 1.20 μg/kg/day for subclinical hypothyroidism (SCH) with TSH ≤ 4.2 mIU/L, 1.42 μg/kg/day for SCH with TSH > 4.2-10 mIU/L, and 2.33 μg/kg/day for overt hypothyroidism (OH) 3
- Adjusting LT4 dose to achieve a TSH level of ≤2.5 mIU/L in the first trimester, as elevated TSH levels are associated with an increased risk of miscarriage 4, 5, 6
- Monitoring TSH levels regularly to ensure that the target level is achieved and maintained throughout pregnancy
LT4 Treatment and Pregnancy Outcomes
Studies have investigated the effects of LT4 treatment on pregnancy outcomes in women with elevated TSH levels:
- LT4 treatment is associated with a decreased risk of pregnancy loss and an increased risk of small-for-gestational-age infants in pregnant women with TSH levels of 2.5-10 mIU/L 6
- LT4 treatment may also be associated with an increased risk of preterm birth in TPOAb-positive pregnant women with high-normal TSH levels 6
- The optimal LT4 dose and treatment strategy may vary depending on individual patient characteristics, such as TPOAb status and TSH level 6
Laboratory Interference and TSH Measurement
It is essential to consider potential laboratory interference when measuring TSH levels: