When should a pregnant woman with hypothyroidism be referred to an obstetrician?

When to Refer Pregnancy with Hypothyroidism to an Obstetrician

Pregnant women with hypothyroidism should be referred to an obstetrician if they have a history of miscarriage, inadequately controlled thyroid function (TSH outside of trimester-specific reference ranges), or require significant dose adjustments during pregnancy. 1

Indications for Referral to an Obstetrician

Mandatory Referrals

• Women with hypothyroidism and a history of miscarriage (high-risk status) 1
• Newly diagnosed hypothyroidism during pregnancy, especially with TSH ≥10 IU/L 1, 2
• Difficulty achieving target TSH levels despite appropriate levothyroxine adjustments
• Signs of pregnancy complications (gestational hypertension, pre-eclampsia)

Consider Referral For

• Women requiring frequent dose adjustments (>25-30% increase from pre-pregnancy dose) 2
• Patients with multiple endocrine disorders
• Patients with poor compliance or absorption issues
• Patients with cardiac disease requiring careful thyroid management 2

Monitoring and Management Prior to Referral

Initial Assessment

• Measure TSH and Free T4 as soon as pregnancy is confirmed 1
• Establish trimester-specific reference ranges for thyroid function tests
• Review current levothyroxine dosage and recent thyroid function tests

Dosage Adjustments

• Most women (up to 75%) require increased levothyroxine dosage during pregnancy 3
• Pre-pregnancy dosage may need to increase by 30% or more by 4-6 weeks gestation 1
• For new onset hypothyroidism with TSH ≥10 IU/L, start at 1.6 mcg/kg/day 2
• For new onset hypothyroidism with TSH <10 IU/L, start at 1.0 mcg/kg/day 2

Monitoring Schedule

• Monitor TSH and Free T4 every 4-6 weeks until TSH levels stabilize 1
• At minimum, check thyroid function during each trimester 1, 2
• Adjust dosage by 12.5-25 mcg increments as needed to maintain normal trimester-specific TSH 2

Clinical Considerations and Pitfalls

Common Pitfalls

• Failure to establish trimester-specific reference ranges for thyroid function tests
• Inadequate dose adjustments during early pregnancy
• Insufficient monitoring frequency
• Not recognizing drug interactions that affect levothyroxine absorption 2
  • Soybean flour, cottonseed meal, walnuts, dietary fiber
  • Iron supplements, calcium supplements
  • Certain medications (antacids, proton pump inhibitors)

Post-Delivery Management

• Reduce levothyroxine dosage to pre-pregnancy levels immediately after delivery 1, 2
• Monitor TSH 4-8 weeks postpartum 2
• Be alert for postpartum thyroiditis, which affects 5-10% of women within the first year after delivery 1

Special Situations Requiring Specialist Care

• Women with adequately treated hypothyroidism before pregnancy have no increased risk of perinatal morbidity 1
• Inadequate or delayed treatment can lead to cognitive impairment in children 1
• Women with a personal or family history of thyroid disease, type 1 diabetes, or autoimmune disorders are at higher risk of postpartum thyroiditis 1

By following these guidelines, primary care providers can appropriately manage pregnant women with hypothyroidism and make timely referrals to obstetricians when necessary, ensuring optimal outcomes for both mother and baby.