From the Guidelines
Pregnant women with hypothyroidism should be treated with levothyroxine to restore the serum TSH concentration to the reference range, with serum TSH concentration monitored every 6 to 8 weeks during pregnancy and the levothyroxine dose modified as needed. This approach is based on the possible association between high TSH and increased fetal wastage or subsequent neuropsychological complications occurring in the offspring due to thyroid insufficiency 1. The requirement for levothyroxine in treated hypothyroid women frequently increases during pregnancy, highlighting the need for regular monitoring and dose adjustments. Key considerations in managing TSH levels in pregnant women with hypothyroidism include:
- Initiating or adjusting levothyroxine therapy to maintain serum TSH within the reference range
- Monitoring serum TSH concentration every 6 to 8 weeks during pregnancy
- Modifying the levothyroxine dose as needed to maintain target TSH levels
- Being aware of the potential for increased levothyroxine requirements during pregnancy The risks of appropriately managed levothyroxine therapy in pregnancy are minimal, and the potential benefits of maintaining normal TSH levels outweigh the risks, particularly in terms of preventing adverse pregnancy outcomes and supporting fetal development 1.
From the FDA Drug Label
Hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, pre-eclampsia, stillbirth and premature delivery. Maternal hypothyroidism may have an adverse effect on fetal and childhood growth and development. During pregnancy, serum T4 levels may decrease and serum TSH levels increase to values outside the normal range Since elevations in serum TSH may occur as early as 4 weeks gestation, pregnant women taking Levothyroxine Sodium Tablets, USP should have their TSH measured during each trimester. An elevated serum TSH level should be corrected by an increase in the dose of Levothyroxine Sodium Tablets, USP Since postpartum TSH levels are similar to preconception values, the Levothyroxine Sodium Tablets, USP dosage should return to the pre-pregnancy dose immediately after delivery. A serum TSH level should be obtained 6-8 weeks postpartum
The optimal management of Thyroid-Stimulating Hormone (TSH) levels in pregnant women with hypothyroidism involves:
- Monitoring TSH levels during each trimester
- Correcting elevated TSH levels by increasing the dose of levothyroxine
- Returning to the pre-pregnancy dose immediately after delivery
- Obtaining a serum TSH level 6-8 weeks postpartum 2
From the Research
Optimal Management of TSH Levels in Pregnant Women with Hypothyroidism
- The optimal management of Thyroid-Stimulating Hormone (TSH) levels in pregnant women with hypothyroidism is crucial to prevent adverse pregnancy outcomes 3.
- Thyroid guidelines recommend a 30 to 50% increase of the preconceptional levothyroxine dose in women with hypothyroidism when pregnancy is diagnosed 4.
- However, some studies suggest that a fixed dose of thyroxine, such as 75 μg/day, may be adequate for most pregnant women with subclinical hypothyroidism, regardless of their weight and baseline TSH level 5.
- Other studies have found that a fixed dose of thyroxine 50 mcg/day may be inadequate in a significant proportion of pregnancy-diagnosed hypothyroidism, and a starting dose of 75 mcg/day may be more adequate 6.
Monitoring and Adjusting TSH Levels
- TSH concentrations should be measured before empirically increasing the levothyroxine dose in pregnant women with autoimmune hypothyroidism 4.
- The dose of thyroxine may need to be increased or decreased based on TSH levels, with a goal of maintaining TSH levels within the desired range 5.
- Increasing the levothyroxine dose in women with uncontrolled hypothyroidism has been associated with a decreased risk of pregnancy loss 3.
Thyroxine Dosage During Pregnancy
- Most hypothyroid patients presenting to an antenatal booking clinic are well-controlled in early pregnancy and will remain so throughout pregnancy, with no change in thyroxine dose required 7.
- However, women who are under-treated before pregnancy may require an increased thyroxine dose and further thyroid function assays 7.