Thyroid Disease Management in Pregnancy

Hyperthyroidism in Pregnancy

The American College of Obstetricians and Gynecologists recommends propylthiouracil (PTU) as the preferred antithyroid medication during the first trimester and methimazole for the second and third trimesters 1, 2
Suppressed TSH with elevated T3 and T4 indicates hyperthyroidism, most commonly due to Graves' disease in pregnancy 1
The goal of treatment is to maintain free T4 or Free Thyroxine Index (FTI) in the high-normal range using the lowest possible thioamide dosage 1, 2
Monitor FT4 or FTI every 2-4 weeks to guide dosage adjustments 1, 2
Untreated maternal hyperthyroidism increases risks of severe preeclampsia, preterm delivery, heart failure, miscarriage, and low birth weight 1, 2

The American College of Obstetricians and Gynecologists recommends treating pregnant women with elevated TSH with levothyroxine to restore TSH to the reference range 3
Levothyroxine requirements often increase during pregnancy, necessitating dose adjustments 3
Monitor serum TSH every 6-8 weeks during pregnancy and modify levothyroxine dose as needed 3

Inform the newborn's physician about maternal thyroid disease due to risk of neonatal thyroid dysfunction 1, 2
Women treated with PTU or methimazole can safely breastfeed 1

Failure to monitor thyroid function regularly during pregnancy may result in inadequate treatment 3, 1
Not switching from PTU to methimazole after the first trimester increases the risk of hepatotoxicity 1, 2
Untreated or inadequately treated thyroid disease can have serious consequences for both mother and fetus 1, 2

The American Family Physician recommends initiating levothyroxine immediately upon diagnosis to normalize TSH and prevent adverse maternal and fetal outcomes, including preeclampsia, low birth weight, and impaired neurodevelopment 4
Untreated maternal hypothyroidism increases risks of preeclampsia, low birth weight, and neuropsychologic defects in offspring, making prompt treatment essential 5, 4

Obtain both TSH and free T4 (or Free Thyroxine Index) for initial diagnosis and monitoring, as recommended by the American Family Physician 5, 4
TSH testing using monoclonal antibodies is the recommended initial screening test, but both TSH and FT4 should be performed when hypothyroidism is suspected 5

Undertreatment poses greater risks than overtreatment during pregnancy, with inadequate treatment associated with low birth weight, preeclampsia, preterm delivery, and impaired neurodevelopment 5, 4