Levothyroxine in Pregnancy: Monitoring, Dosing, and Safety

Levothyroxine (LT4) is the standard treatment for hypothyroidism in pregnancy. It is category A (no fetal risk) and does not cross the placenta significantly.

Critical Management Points

• Preconception: Optimize TSH (target 0.5–2.5 mIU/L) before conception.
• Early pregnancy: Dose often needs 25–50% increase by 4–6 weeks; check TSH at confirmation and every 4 weeks until mid‑pregnancy.
• Trimester‑specific TSH targets:
  • 1st: 0.1–2.5 mIU/L
  • 2nd: 0.2–3.0 mIU/L
  • 3rd: 0.3–3.0 mIU/L
• Postpartum: Reduce to pre‑pregnancy dose; recheck TSH at 6 weeks.
• Brand consistency: Avoid switching formulations without monitoring.

Why It Matters

Maternal hypothyroidism increases miscarriage, preterm birth, preeclampsia, and impaired fetal neurocognitive development. Adequate treatment mitigates these risks.