What are the potential complications to watch for in a newborn delivered by Normal Spontaneous Vaginal Delivery (NSVD) to a mother with Graves' disease taking Propylthiouracil (PTU)?

Neonatal Monitoring After Maternal Graves' Disease and PTU Exposure

Critical Immediate Assessment

Monitor this newborn closely for both neonatal hyperthyroidism (from transplacental maternal TSH receptor antibodies) and transient hypothyroidism (from PTU exposure), as both conditions can occur sequentially and cause significant morbidity if untreated. 1, 2, 3

Primary Thyroid Complications to Monitor

Neonatal Hyperthyroidism (Most Critical)

• Measure TSH receptor antibodies (TRAb) in cord blood or as soon as possible after delivery - this is the key risk stratification tool 3

  • If maternal TRAb was elevated during pregnancy (particularly >200 IU/L), the newborn is at high risk for immune-mediated hyperthyroidism 4
  • Maternal antibodies cross the placenta maximally by 30 weeks and persist in the neonate for weeks to months after delivery 5

• Obtain baseline thyroid function tests (free T4 and TSH) at day 3-5 of life, then repeat at day 10-14 3

  • Do NOT rely on cord blood TSH/T4 levels for initial assessment 3
  • Continue clinical monitoring until 2-3 months of age, as hyperthyroidism may develop late as PTU effects wear off 6, 3

• Watch for clinical signs of neonatal thyrotoxicosis:

  • Persistent tachycardia (>160 bpm at rest) - most sensitive early sign 6, 5
  • Poor weight gain despite increased appetite, irritability, tremors 5
  • Goiter (palpable thyroid enlargement) 5
  • Exophthalmos, lid lag 5
  • Heart failure (12-20% mortality if untreated) 5

Transient Hypothyroidism (From PTU Exposure)

• PTU crosses the placenta and can suppress fetal thyroid function 2

  • Cord blood may show low free T4 and elevated TSH initially 7
  • This typically resolves spontaneously within days to weeks as PTU is cleared from the neonatal system 7, 3

• Central hypothyroidism can also occur in these infants - be alert for low T4 with inappropriately normal/low TSH 3

Secondary Complications

Hepatotoxicity Risk

• The FDA reports cases of in utero PTU exposure causing neonatal liver failure and death 2
  • Monitor for signs of hepatic dysfunction: jaundice beyond physiologic levels, poor feeding, lethargy 2
  • Consider baseline liver function tests if clinically indicated, though routine screening is not standard 2

Fetal Goiter Complications

• Assess airway patency immediately after delivery - goiter can cause tracheal compression and respiratory distress 5, 8
• Large goiters may have caused dystocia during delivery 8

Other Rare Manifestations

• Hydrops fetalis has been reported with severe fetal hypothyroidism from PTU exposure, though this would typically be detected prenatally 8
• Thrombocytopenia, growth restriction 5

Management Algorithm

If TRAb Negative:

• No specific thyroid follow-up needed beyond routine newborn care 3

If TRAb Positive or Unavailable:

1. Days 3-5: Obtain free T4 and TSH 3

   • If biochemically hyperthyroid with symptoms → start methimazole (NOT PTU in neonates) 3
   • If asymptomatic with mild elevation → clinical judgment; close monitoring acceptable 3

2. Days 10-14: Repeat free T4 and TSH 3

   • Hyperthyroidism may emerge as maternal PTU effect wanes 6, 7

3. Weekly monitoring if on treatment until stable, then every 1-2 weeks 3

   • Treatment typically needed for 1-2 months as maternal antibodies clear 3

4. Continue clinical surveillance until 2-3 months of age even if biochemically normal 3

Treatment Considerations if Hyperthyroidism Develops:

• Methimazole is the antithyroid drug of choice for neonates (not PTU due to hepatotoxicity risk) 3
• Add propranolol for symptomatic tachycardia/irritability 3
• Potassium iodide reserved for refractory cases 3

Critical Pitfall to Avoid

Do not assume the newborn is safe based on normal cord blood values or initial testing - neonatal hyperthyroidism commonly develops 4-5 days after delivery as PTU levels decline while maternal TRAb persists 6, 7. The American Academy of Family Physicians emphasizes that the newborn's physician must be informed about maternal Graves' disease specifically because of this delayed presentation risk 1, 9.