Pregnancy — the Importance
of TSH Management7
Management of thyroid diseases during pregnancy requires special considerations because pregnancy can induce major changes in thyroid function.
Serum TSH values should be obtained early in pregnancy in the following women at high risk for overt hypothyroidism:
- History of thyroid dysfunction or prior thyroid surgery
- Age >30 years
- Symptoms of thyroid dysfunction or the presence of goiter
- TPOAb positivity
- Type 1 diabetes or other autoimmune disorders
- History of miscarriage or preterm delivery
- History of head or neck radiation
- Family history of 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 their dose adjusted by their provider in order to optimize serum TSH values.
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 because further LT4 dose adjustments are often required.
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. This calls for pregnancy-specific and ideally trimester-specific reference intervals for all thyroid function tests but in particular for the most widely applied tests, TSH and free T4 (FT4).
If trimester-specific reference ranges for TSH are not available in the laboratory, the following reference ranges are recommended: