The Thyroid and Pregnancy Francis S. Greenspan March 19, 2010 OUTLINE OF DISCUSSION 1. Normal Physiology 2. Hypothyroidism 3. Hyperthyroidism 4. Thyroid Nodules and Cancer NORMAL PHYSIOLOGY Iodine Requirements: USA Average intake: 150 mcg/d. Recommended: 250 mcg/d Fetus requires T4 for optimal Brain development: Derived from Mother 1 st trimester, then endogenous. 30-50% Increase T4 requirement with onset pregnancy Initially derived from HcG stimulation of thyroid gland Increased TBG maintains high T4 level Monitor: Total T4, TSH 1
Maternal Thyroid Function in Pregnancy Burrow GN et al. N Eng J Med 331: 1072, 1994. Copyright 1994, Massachusetts Med Soc, all rights reserved HYPOTHYOIDISM AND PREGNANCY Incidence: Overt 0.3-0.5%, Subclinical 2-3%, Antibody + 5-15% Maternal: Relative infertility, spontaneous abortion, anemia, hypertension, hemorrhage, placental abruption Fetal: Premature birth, low birth weight, neonatal respiratory distress, impaired neuropsychological development with low IQ scores and learning disabilities HYPOTHYROIDISM AND PREGNANCY RISK FACTORS History Thyroidectomy or Radioiodine Therapy On T4 Rx, previous diagnosis Hypothyroidism Family History Thyroid disease Positive thyroid autoantibodies DIAGNOSIS T4 < 8mcg/dl, TSH >3 mul THERAPY Increase T4 dose 25-50%. Goal: T4 10-14 mcg/dl, TSH 0.5-2 mu/l 2
HYPERTHYROIDISM AND PREGNANCY Incidence: 0.1-0.4%, 85% Graves Disease Other causes: Toxic nodular goiter, thyroiditis, hyperemesis gravidarum Diagnosis: History previous episode, poor weight gain, tachycardia, goiter, eye signs, GI symptoms Lab: T4 >14 mcg/dl, T3 >220 ng/dl, TSH < 0.1 mu/l., TSI > 125% HYPERTHYROIDISM AND PREGNANCY Premature delivery, preeclampsia, heart failure, thyroid storm low birth weight, stillbirth Antithyroid drug therapy: PTU preferred because of rare fetal complications (aplasia cutis, choanal/esophageal atresia) with Methimazole. Use lowest possible PTU dose, 100-200 mg/d initially and 25-50 mg/d for maintenance. Other Options: Middle trimester thyroidectomy for large toxic goiter or drug reaction. Prepare with propanolol and iodide. PO T4. Hyperemesis Gravidarum Definition: Severe nausea and vomiting with weight loss >5% of prepregnant weight Etiology: Asociated with HcG >200U/ml. Rule out: Graves Disease (high TSI), GI, Renal disease, Hydatiform Mole Supportive therapy, spontaneous remission by 14-20 weeks Encephalopathy, hepatic or renal failure, poor fetal growth 3
Neonatal Graves Disease Etiology: Transplacental passage of maternal TSI. Maternal TSI usually >400% (normal <125%) Presentation: 1-3 days after delivery infants develop hyperthyroidism with prominent eyes, tachycardia, goiter, congestive heart failure. They are small for gestational age, and have accelerated bone age and craniosynostoses. Lab: High FT4, FT3, suppressed TSH, elevated TSI Usually by Neonatologist, PTU, KI, propanolol, supportive therapy Usually subsides spontaneously in 6-12 weeks but may continue as active Graves Disease for months. Thyroid Nodules and Cancer Prevalence of Thyroid Nodules: Varies with iodine sufficiency and exam technique Estimate 5-15% Risk Assessment: High Risk: Radiation exposure, Family History, Recent growth, hoarseness, dysphagia Lab: TSH, T4, T3, Thyroperoxidase antibodies Thyroid Ultrasound FNA Biopsy of suspicious Nodules Thyroid Nodules and Cancer Management Benign Thyroid Nodules: Watch for growth or toxicity. Repeat biopsy 1 year Malignant Nodule: Plan Thyroidectomy after delivery. If aggressive or obstructive consider thyroidectomy middle trimester Consider T4 therapy to keep TSH < 0.5 mu/l Hold radioiodine therapy until pregnancy and nursing are completed 4
SUMMARY 1. Normal Physiology: Adequate iodine intake essential TSH suppression due to HCG effect Rise in T4 and T3 due TBG 2. Hypothyroidism: Increased delivery T4 essential for fetal brain development 3. Hyperthyroidism: PTU therapy preferred because of teratogenecity of Methimazole High levels of TSI can induce neonatal Graves Disease 4. Nodules and Cancer: FNA Biopsy critical for diagnosis Surgery and radioiodine therapy for cancer can be postponed until after delivery 5