What are the guidelines for maternal care, management, and surveillance, as well as fetal surveillance, in the management of hypothyroidism (underactive thyroid) during pregnancy?

From the Guidelines

Management of hypothyroidism during pregnancy requires careful maternal and fetal surveillance to ensure optimal outcomes, with a focus on maintaining TSH levels within the reference range to minimize adverse pregnancy outcomes, as supported by the most recent evidence 1. For maternal care, women with pre-existing hypothyroidism should increase their levothyroxine dose by approximately 30-50% as soon as pregnancy is confirmed, typically by taking two extra doses weekly.

• Thyroid function tests (TSH and free T4) should be monitored every 4-6 weeks during the first trimester and at least once during the second and third trimesters, with TSH targets of <2.5 mIU/L in the first trimester and <3.0 mIU/L in later trimesters, as recommended by recent guidelines 1.
• Dose adjustments should be made promptly to maintain these targets, as maternal hypothyroidism can lead to adverse pregnancy outcomes including miscarriage, preeclampsia, and impaired fetal neurodevelopment, highlighting the importance of close monitoring and management 1. For fetal surveillance, regular ultrasounds should be performed to assess fetal growth, amniotic fluid volume, and anatomical development, with particular attention to cardiac function and central nervous system development.
• In cases of poorly controlled maternal hypothyroidism, more frequent fetal assessment may be warranted, including non-stress tests and biophysical profiles in the third trimester, to ensure optimal fetal outcomes 1. After delivery, most women can return to their pre-pregnancy levothyroxine dose, with thyroid function reassessment at 6 weeks postpartum, as the requirement for levothyroxine often decreases after pregnancy, as noted in earlier studies 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. 2

From the Research

Maternal Care, Management, and Surveillance

• Maternal care for hypothyroidism during pregnancy involves optimizing treatment to reduce adverse fetal and maternal outcomes 3.
• Women with a history of hypothyroidism or risk factors should have preconception care to ensure euthyroidism from the onset of pregnancy, with a TSH target of below 2.5mIU/L 3.
• Levothyroxine doses should be titrated against TSH, which have trimester-specific ranges, and an empirical dose increase of 30-50% may be considered as soon as pregnancy is confirmed 3, 4.
• For women with newly diagnosed overt hypothyroidism in pregnancy, starting doses of either 100 or 150 mg daily may be considered safe 3.
• Surveillance of thyroid function is needed throughout gestation to make dose adjustments when needed, and many women require more thyroxine during pregnancy 5, 6.

Fetal Surveillance

• Fetal surveillance is crucial in pregnancies complicated by hypothyroidism, as untreated or undertreated hypothyroidism can lead to adverse fetal outcomes 4, 5.
• Proper therapy can eliminate or reduce the risk of complications, such as pregnancy-induced hypertension, preterm delivery, and prematurity 5.
• However, overtreatment with levothyroxine in pregnancy has been associated with preterm delivery, highlighting the need for careful management of thyroid replacement therapy 7.
• The relationship between maternal hypothyroidism and fetal outcomes is complex, and further research is needed to fully understand the effects of hypothyroidism on fetal development and well-being 7, 6.