What are the management and surveillance strategies for maternal care and fetal surveillance in a pregnant woman with Hashimoto's (Autoimmune) hypothyroidism?

From the Guidelines

Hashimoto's hypothyroidism during pregnancy should be managed with levothyroxine (LT4) to maintain TSH levels within the reference range, with dosage adjustments made every 6-8 weeks as needed, to minimize risks of fetal wastage and neuropsychological complications in the offspring. For maternal care, the goal is to maintain TSH levels below 2.5 mIU/L in the first trimester and below 3.0 mIU/L in the second and third trimesters, as untreated or poorly controlled maternal hypothyroidism can lead to impaired fetal neurocognitive development, preterm birth, low birth weight, and increased risk of miscarriage 1. Some key points to consider in maternal care include:

• Levothyroxine dosage typically needs to be increased by 30-50% as soon as pregnancy is confirmed, and women already on levothyroxine before pregnancy often need dose increases within the first 4-8 weeks of gestation due to increased thyroid hormone requirements.
• Thyroid function tests should be checked every 4-6 weeks throughout pregnancy, with dose adjustments made promptly to maintain optimal levels.
• The requirement for levothyroxine in treated hypothyroid women frequently increases during pregnancy, and the risks of appropriately managed levothyroxine therapy in pregnancy are minimal 1. For fetal surveillance, regular ultrasounds should be performed to monitor fetal growth and development, particularly at 18-22 weeks for anatomical assessment, as maternal levothyroxine does not significantly cross the placenta 1. Some key points to consider in fetal surveillance include:
• No direct fetal thyroid testing is typically needed.
• Untreated or poorly controlled maternal hypothyroidism can lead to impaired fetal neurocognitive development, preterm birth, low birth weight, and increased risk of miscarriage, making strict maternal thyroid control essential.
• Women who are adequately treated before pregnancy and those diagnosed and treated early in pregnancy have no increased risk of perinatal morbidity 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. Monitor TSH every 4 weeks until a stable dose is reached and serum TSH is within normal trimester-specific range. Reduce levothyroxine sodium dosage to pre-pregnancy levels immediately after delivery. Monitor serum TSH 4 to 8 weeks postpartum.

Maternal Care and Management:

• Measure serum TSH and free-T4 as soon as pregnancy is confirmed and during each trimester.
• Maintain serum TSH in the trimester-specific reference range.
• Monitor TSH every 4 weeks until a stable dose is reached.
• Adjust levothyroxine sodium dosage as needed to maintain normal trimester-specific range.

Fetal Surveillance:

• No direct information is provided in the drug label regarding fetal surveillance for pregnant patients with Hashimoto's hypothyroidism. 2

From the Research

Maternal Care, Management, and Surveillance

• Maternal care for Hashimoto's hypothyroidism during pregnancy involves managing thyroid hormone levels to prevent adverse effects on the mother and the fetus 3, 4.
• Thyroid function tests should be interpreted with regard to gestational age, and overt hypothyroidism should be promptly treated regardless of the thyroid-stimulating hormone (TSH) level 5.
• Women with pre-existing treated hypothyroidism may require an increase in levothyroxine (LT4) dosing to maintain euthyroidism during gestation, and close monitoring of serum TSH levels is necessary to avoid overtreatment or undertreatment 5.
• The management of Hashimoto's thyroiditis during pregnancy should focus on controlling symptoms, and the use of levothyroxine (LT4) is recommended, with the dose based on the degree of preserved thyroid functionality and lean body mass 6.

Fetal Surveillance

• Fetal surveillance is crucial in pregnancies complicated by Hashimoto's hypothyroidism, as thyroid dysfunction can adversely affect obstetric outcomes 3.
• The presence of thyroid autoantibodies, such as thyroid peroxidase antibodies (TPOAbs), is associated with an increased risk of recurrent miscarriages and preterm birth in pregnant women 6.
• Fetal surveillance should include regular monitoring of fetal growth and development, as well as monitoring for signs of fetal distress or other complications 4.
• The use of levothyroxine (LT4) during pregnancy is recommended to maintain euthyroidism and prevent adverse effects on the fetus, and the dose should be adjusted based on serum TSH levels and fetal surveillance 5.