Is it safe to take Synthroid (levothyroxine) while pregnant?

Taking Synthroid (Levothyroxine) During Pregnancy

Yes, it is safe and often necessary to take Synthroid (levothyroxine) during pregnancy, and the dosage typically needs to be increased early in pregnancy to maintain proper thyroid function.

Safety and Importance of Levothyroxine During Pregnancy

• Levothyroxine is safe during pregnancy and should not be discontinued, as untreated hypothyroidism can lead to adverse maternal and fetal outcomes 1, 2
• The FDA classifies levothyroxine as safe for use during pregnancy, noting that clinical experience "have not reported increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes" 2
• Hypothyroidism during pregnancy is associated with increased risks of miscarriage, gestational hypertension, preeclampsia, stillbirth, premature delivery, and adverse effects on fetal neurocognitive development 2, 3

Dosage Adjustments During Pregnancy

• Pregnancy increases levothyroxine requirements in most women treated for hypothyroidism, often beginning as early as the fifth week of gestation 4
• The dosage typically needs to be increased by approximately 30-50% during pregnancy, with most of this increase occurring in the first trimester 4, 5
• According to guidelines, levothyroxine dosage needs to be adjusted for proper neurologic development of the fetus 1
• Frequent monitoring of thyroid function is essential during pregnancy, as many women demonstrate an increased requirement for thyroid hormone during the first trimester 5

Monitoring Protocol During Pregnancy

• Serum TSH levels should be monitored and levothyroxine dosage adjusted throughout pregnancy 2
• Check thyroid function tests every 4-6 weeks during the first half of pregnancy and at least once during the second half 6, 5
• The goal is to maintain TSH in the normal range specific for pregnancy (generally lower than non-pregnant ranges) 7
• After delivery, the levothyroxine dosage should typically return to the pre-pregnancy dose 2

Special Considerations

• For women newly diagnosed with hypothyroidism during pregnancy, treatment should be initiated promptly to minimize risks 8
• For subclinical hypothyroidism (elevated TSH with normal T4), treatment is still recommended during pregnancy to prevent adverse outcomes 6, 7
• Women with hypothyroidism who are planning pregnancy should have their thyroid function optimized before conception 1, 3

Common Pitfalls to Avoid

• Failing to increase levothyroxine dose early enough in pregnancy can lead to maternal hypothyroidism and potential adverse effects on fetal development 4
• Undertreatment risks include persistent hypothyroid symptoms, adverse effects on cardiovascular function, and negative impacts on fetal development and quality of life 6
• Overtreatment with excessive doses could potentially lead to iatrogenic hyperthyroidism, which carries its own risks 6
• Waiting until symptoms develop before adjusting the dose is not recommended, as physiological changes in pregnancy necessitate proactive dose adjustments 5, 4

Remember that maintaining proper thyroid function throughout pregnancy is crucial for both maternal health and optimal fetal development, particularly neurological development. Regular monitoring and appropriate dose adjustments are essential components of care.