What are the recommended Thyroid-Stimulating Hormone (TSH) levels for women trying to conceive or during pregnancy?

From the Guidelines

For women trying to conceive or during pregnancy, the recommended Thyroid-Stimulating Hormone (TSH) levels should be maintained below 2.5 mIU/L, with ideal ranges between 0.4-2.5 mIU/L before conception and during the first trimester, and less than 3.0 mIU/L in the second and third trimesters. This recommendation is based on the potential association between high TSH and increased fetal wastage or subsequent neuropsychological complications occurring in the offspring due to thyroid insufficiency, as noted in a study published in JAMA 1. If hypothyroidism is detected, treatment with levothyroxine is typically prescribed, with the starting dose depending on the severity of hypothyroidism and body weight, usually ranging from 25-100 mcg daily, taken on an empty stomach 30-60 minutes before breakfast.

During pregnancy, thyroid medication needs may increase by approximately 30-50%, often requiring dose adjustments, and TSH levels should be checked every 6 to 8 weeks during pregnancy, as recommended by the study 1. Proper thyroid function is crucial during conception and pregnancy because thyroid hormones play essential roles in fetal brain and nervous system development. Untreated hypothyroidism can increase risks of miscarriage, preeclampsia, anemia, postpartum hemorrhage, and neurodevelopmental issues in the baby. Women with pre-existing thyroid conditions should consult their healthcare provider before conception to optimize thyroid levels. The most recent guidelines from the U.S. Preventive Services Task Force recommend against screening for thyroid dysfunction in non-pregnant adults, but this does not apply to pregnant women or those trying to conceive, as noted in studies published in Annals of Internal Medicine 1.

Some key points to consider include:

• TSH levels should be monitored regularly during pregnancy to ensure optimal thyroid function
• Levothyroxine treatment should be adjusted as needed to maintain TSH levels within the recommended range
• Women with pre-existing thyroid conditions should work closely with their healthcare provider to manage their condition during pregnancy
• Untreated hypothyroidism can have significant consequences for both the mother and the fetus, making proper management essential.

From the FDA Drug Label

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. Monitor TSH every 4 weeks until a stable dose is reached and serum TSH is within normal trimester-specific range.

The recommended Thyroid-Stimulating Hormone (TSH) levels for women trying to conceive or during pregnancy are to be maintained in the trimester-specific reference range. However, the exact TSH values for this range are not specified in the provided drug label. 2

From the Research

TSH Levels During Pregnancy and Conception

• The recommended Thyroid-Stimulating Hormone (TSH) levels for women trying to conceive or during pregnancy is ≤2.5 mIU/L, as established by current guidelines 3.
• A study found that there is no distinct range of TSH ≤2.5 mIU/L for infertile women undergoing in vitro fertilization (IVF) that improves reproductive outcomes, suggesting that the recommended TSH range for pregnancy may be applied to infertile patients attempting conception without a need for further adjustment 3.
• For adults with subclinical hypothyroidism, thyroid hormones consistently demonstrate no clinically relevant benefits for quality of life or thyroid-related symptoms, and the guideline panel issues a strong recommendation against thyroid hormones in adults with subclinical hypothyroidism, except for women who are trying to become pregnant or patients with TSH >20 mIU/L 4.

TSH Levels and Thyroid Hormone Replacement

• Levothyroxine is frequently prescribed for hypothyroidism, and understanding the impact of patient weight and residual thyroid function on initial levothyroxine dosage is crucial for consistently maintaining euthyroidism 5.
• A trial of combination therapy with levothyroxine and liothyronine may be beneficial for patients not restored to baseline health with levothyroxine, but this is not supported by the majority of randomized clinical trials, and monitoring for adverse effects is necessary 5.
• Reverse T3 (rT3) levels were found to be elevated in patients with symptoms of fatigue on various thyroid hormone replacements, with the highest levels of rT3 in those taking L-T4 replacement alone and the lowest levels of rT3 in those on preparations that contained L-T3 alone 6.

Key Findings

• The recommended TSH range for pregnancy (≤2.5 mIU/L) may be applied to infertile patients attempting conception without a need for further adjustment 3.
• Thyroid hormones consistently demonstrate no clinically relevant benefits for quality of life or thyroid-related symptoms in adults with subclinical hypothyroidism, except for women who are trying to become pregnant or patients with TSH >20 mIU/L 4.
• Combination therapy with levothyroxine and liothyronine may be beneficial for patients not restored to baseline health with levothyroxine, but monitoring for adverse effects is necessary 5.