Pregnancy — the Importance
of TSH Management7
The 2017 American Thyroid Association guidelines provide recommendations for the management of hypothyroidism and TSH during pregnancy
Management of thyroid diseases during pregnancy requires special considerations because pregnancy can induce major changes in thyroid function.
Serum TSH values should be obtained as soon as pregnancy is confirmed in the following women at high risk for thyroid disease:
- A history of hypothyroidism/hyperthyroidism or current symptoms/signs of thyroid dysfunction
- Known thyroid antibody positivity
- Presence of goiter
- History of head or neck radiation or prior thyroid surgery
- Age > 30 years
- History of Type 1 diabetes or other autoimmune disorders
- History of pregnancy loss, preterm delivery, or infertility
- Multiple prior pregnancies (≥2)
- Family history of autoimmune thyroid disease or thyroid dysfunction
- Morbid obesity (BMI ≥ 40 kg/m2)
- Use of amiodarone or lithium, or recent administration of iodinated radiologic contrast
- Residing in an area of known moderate to severe iodine insufficiency
Recommendation BEFORE Pregnancy
Treated hypothyroid patients (receiving LT4) who are planning pregnancy should have serum TSH evaluated preconception and their LT4 dose adjusted to achieve a TSH value between the lower reference limit and 2.5 mU/L.
Recommendation DURING Pregnancy
In pregnant patients with treated hypothyroidism, maternal serum TSH should be monitored approximately every 4 weeks during the first half of pregnancy and at least once near 30 weeks gestation, because further LT4 dose adjustments may be required.
For patients with serum TSH above the normal trimester-specific range, increase the dose of Synthroid by 12.5 to 25 mcg/day and measure TSH every 4 weeks until a stable Synthroid dose is reached and serum TSH is within the normal trimester-specific range.
Recommendation AFTER Pregnancy
The necessary LT4 dose adjustments during gestation are a function of pregnancy itself. Therefore, following delivery, LT4 should be reduced to the patient’s preconception dose. Additional TSH testing should be performed at approximately 6 weeks postpartum.
Thyroid Function Test
Thyroid function test results of healthy pregnant women differ from those of healthy nonpregnant women, as well as by population.
Population and trimester-specific reference ranges for serum TSH during pregnancy should be used, determined by each provider's institute/laboratory.
If not feasible, apply pregnancy-specific TSH reference ranges for similar patient populations under similar conditions.
If neither internal nor transferable pregnancy-specific TSH reference ranges are available, an upper reference limit of ~4.0 mU/L may be used.
When treating hypothyroidism in pregnant women, consider a target TSH in the lower half of the trimester-specific reference range. If unavailable, strive for TSH values below 2.5 mU/L.