What are the guidelines for perioperative management of hypothyroidism (underactive thyroid) in pregnancy?

Perioperative Management of Hypothyroidism in Pregnancy

Immediate Preoperative Assessment and Optimization

For pregnant women with known hypothyroidism requiring surgery, ensure TSH is maintained below 2.5 mIU/L before any elective procedure, and continue levothyroxine throughout the perioperative period without interruption. 1, 2

Critical Pre-Surgical Considerations

• Verify current thyroid status by measuring TSH and Free T4 immediately if not checked within the past 4 weeks, as pregnancy increases levothyroxine requirements in over 50% of women with pre-existing hypothyroidism 3, 4
• Do not delay emergency surgery for thyroid optimization, but recognize that untreated hypothyroidism increases risks of preeclampsia, low birth weight, and impaired fetal neuropsychological development 1
• Rule out adrenal insufficiency before initiating or adjusting levothyroxine, as starting thyroid hormone before corticosteroids can precipitate adrenal crisis 5

Levothyroxine Management During Perioperative Period

Continuation of Therapy

• Continue levothyroxine on the day of surgery - the medication has a long half-life and missing doses perioperatively can destabilize thyroid status 6
• Administer levothyroxine orally when the patient resumes oral intake, typically within hours after most procedures 6
• For prolonged NPO status (>3-5 days), consider IV levothyroxine at 75% of the oral dose, though this is rarely necessary for routine surgical procedures 6

Dose Adjustments Based on Current Status

If TSH is elevated (>2.5 mIU/L) preoperatively:

• Increase levothyroxine dose by 12.5-25 mcg immediately 1, 6
• For TSH >10 mIU/L, increase by 25-50 mcg to rapidly achieve euthyroidism 5, 7
• Recheck TSH 4 weeks postoperatively to ensure adequate control 1, 6

If patient is newly diagnosed with hypothyroidism during pregnancy:

• Start levothyroxine 100-150 mcg daily for overt hypothyroidism (TSH ≥10 mIU/L) 7
• Start levothyroxine 1.0 mcg/kg/day for TSH <10 mIU/L 6
• Monitor TSH every 4 weeks and adjust to maintain TSH <2.5 mIU/L 1, 2

Trimester-Specific Monitoring Protocol

First Trimester (Most Critical Period)

• Increase levothyroxine by 30% immediately upon pregnancy confirmation if patient has pre-existing hypothyroidism, as requirements increase as early as 5 weeks gestation 4, 7
• Target TSH <2.5 mIU/L throughout first trimester to prevent adverse fetal neurodevelopmental outcomes 1, 2
• Monitor TSH every 4 weeks during pregnancy until stable, then at minimum once per trimester 1, 6

Second and Third Trimesters

• Maintain TSH within trimester-specific ranges (generally <3.0 mIU/L for second and third trimesters) 3
• Continue monitoring every 4 weeks if dose adjustments are needed 1, 6
• Maintain Free T4 in upper half of normal range to ensure adequate fetal thyroid hormone supply 8, 1

Special Perioperative Scenarios

Emergency Surgery

• Proceed with surgery regardless of thyroid status - do not delay life-saving procedures 1
• Start or continue levothyroxine immediately postoperatively at appropriate pregnancy doses 6, 7
• Monitor more closely with TSH and Free T4 at 2-4 weeks post-surgery rather than standard 4-8 weeks 6

Cardiac Surgery or High-Risk Procedures

• Use lower starting doses (25-50 mcg daily) if initiating levothyroxine in patients with cardiac disease, then titrate every 6-8 weeks 5, 6
• Monitor for cardiac complications as untreated hypothyroidism can cause delayed relaxation and abnormal cardiac output 5
• Avoid overtreatment which increases risk of atrial fibrillation, particularly concerning during pregnancy 5

Critical Pitfalls to Avoid

• Never discontinue levothyroxine perioperatively - this is the most common and dangerous error, as TSH can rise rapidly during pregnancy 1, 4
• Do not use preconception doses - pregnancy increases requirements by 30-50% on average, with increases needed as early as 5 weeks gestation 4, 7
• Avoid treating isolated maternal hypothyroxinemia (low T4, normal TSH) differently - this condition also requires levothyroxine to restore T4 to normal range due to fetal neurodevelopmental risks 8
• Do not wait for "optimal" TSH before elective surgery - if TSH is mildly elevated (2.5-10 mIU/L), proceed with surgery and optimize postoperatively, as delays pose greater risks 1, 2

Postoperative Management

Immediate Postpartum Period

• Reduce levothyroxine to pre-pregnancy dose immediately after delivery 6, 9
• Recheck TSH at 4-8 weeks postpartum to confirm appropriate dosing 6, 9
• Reassess need for continued therapy if hypothyroidism was diagnosed during pregnancy, as some cases may be transient 8

Post-Surgical Follow-Up

• Monitor TSH 4 weeks after any perioperative dose adjustment 1, 6
• Continue pregnancy-appropriate monitoring schedule (every 4 weeks) until delivery if surgery occurred during pregnancy 1
• Maintain Free T4 in upper normal range throughout remainder of pregnancy 8, 1