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Thyroid disorders and pregnancy. Medical Complications November 23, 2007 Jill Newstead-Angel, MD FRCPC. Objectives. Discuss the normal physiology of the thyroid gland during pregnancy Discuss hyperthyroidism and pregnancy Diagnosis Treatment Discuss hypothyroidism and pregnancy

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thyroid disorders and pregnancy

Thyroid disorders and pregnancy

Medical Complications

November 23, 2007

Jill Newstead-Angel, MD FRCPC

objectives
Objectives
  • Discuss the normal physiology of the thyroid gland during pregnancy
  • Discuss hyperthyroidism and pregnancy
    • Diagnosis
    • Treatment
  • Discuss hypothyroidism and pregnancy
    • Diagnosis
    • Treatment
  • Discuss thyroid nodules in pregnancy
case 1
Case 1
  • 24 yr old G2P1 presents at 9 weeks GA for first prenatal visit
  • Part of screening blood work was TSH
  • TSH 0.5 mU/L
  • Clinically and on history - no evidence of thyroid disease
what should be done
What should be done?
  • Book the patient for a radioactive iodine uptake scan
  • Start PTU at 100 mg bid
  • Do nothing at all
  • Check FT4 and FT3
normal thyroid physiology in pregnancy
Normal thyroid physiology in pregnancy
  • Fetal thyroid and fetal hypothalamic-pituitary-thyroid axis develop independently of maternal thyroid
    • Starts to function after 10 weeks GA
    • 11-12 weeks GA, fetal thyroid concentrates iodine and FT4 and TSH are present in fetal circulation
slide6
Increase in thyroid binding globulin due to increase in estrogen (stimulation of hepatic production and decreased degradation)
    • Increase in total T4 and T3
  • Increase in GFR leads to increase in renal iodine clearance
slide7
HCG has similar properties to TSH therefore has intrinsic thyroid stimulating activity
    • increase FT4 and FT3 levels during first trimester
increase frequency in goiters
Increase frequency in goiters?
  • In iodine replete areas there is not an increased frequency of goiters during pregnancy
  • If there is a palpable goiter - should be further investigated as underlying thyroid disease is present 50% of the time
hyperemesis gravidarum
Hyperemesis Gravidarum
  • High levels of HCG
  • Associated biochemical evidence of hyperthyroidism
  • Does not need treatment
  • Follow patients out of first trimester to ensure not true hyperthyroidism
what should be done11
What should be done?
  • Book the patient for a radioactive iodine uptake scan
  • Start PTU at 100 mg bid
  • Do nothing at all
  • Check FT4 and FT3
case 2
Case 2
  • 33 year old G5P4 presents at 13 weeks GA for first prenatal
  • Complaining of palpitations, heat intolerance, and tremors
  • Clinically: tachycardia, tremor and palpable thyroid with bruit
slide13
TSH <0.01
  • FT4 33
  • FT3 9
hyperthyroidism and pregnancy
Hyperthyroidism and pregnancy
  • Prevalence 0.1 to 0.4%
  • Graves is the most common cause
    • Other causes:
      • Functioning adenoma
      • Toxic mutlinodular goiter
      • Thyroiditis
      • Excessive thyroid hormone intake
      • Gestational transient thyrotoxicosis
slide15
Diagnosis difficult in pregnancy because of the hyper dynamic state of pregnancy
    • Eye signs, tremor, weight loss, marked tachycardia more suggestive of hyperthyroidism
  • Laboratory
    • low TSH with elevated FT4 and FT3
    • TSH receptor antibodies
    • TPO and TBG antibodies
pregnancy outcome
Pregnancy outcome
  • Depends on treatment and control
  • Worse pregnancy outcomes with no treatment or partial treatment
    • Preterm labor
    • Preeclampsia
    • Stillbirth
    • Small for gestational age
treatment
Treatment
  • Antithyroid medications
    • PTU
      • partially inhibits the conversion of T4 to T3
      • Crosses the placenta less
      • Dose 100 – 600 mg
    • Methimazole
      • Aplasia cutis
      • Dose 10 – 40 mg
      • Transient leukopenia develops 10% women treated
  • Beta blockers
    • Propranolol - may be useful in those with marked tachycardia
slide18
Surgery
    • Second trimester best
    • Reserved for those that fail medical treatment
  • Radioactive iodine treatment
    • Contraindicated in pregnancy
  • Over all goal
    • treat maternal disease while limiting potential for fetal hypothyroidism
back to case
Back to case
  • Send off blood work for Thyroid stimulating antibodies
  • Start PTU 100 mg tid
  • Start propanolol 10 - 20 mg bid
  • Repeat TSH in 2 weeks
  • Titrate medications to keep FT4 within higher limits of normal
slide21

Sub-clinical hyperthyroidism

  • Low TSH with normal FT4
  • Affects 1.7% of pregnant women
  • During pregnancy – not found to be associated with any adverse outcomes
case 3
Case 3
  • 25 year old G1P1 seen preconception for hypothyroidism
  • Would like to conceive in the near future
  • Currently on Synthyroid 75 mcg per day
  • Most recent TSH 4 with normal FT4 and FT3
slide23

Hypothyroidism and pregnancy

  • 95% the result of primary disease of the thyroid
    • Autoimmune (Hashimoto’s thyroiditis)
  • Less common causes
    • Over treatment of hyperthyroidism
    • Transient hypothyroidism due to postpartum thyroiditis
    • Medications
    • Pituitary or hypothalamic disease
diagnosis
Diagnosis
  • 20-30% of patients have symptoms
  • Elevated TSH
  • Patients with central hypothyroidism do not manifest elevated TSH during pregnancy
slide25

Complications

  • Overt hypothyroidism
    • Gestational hypertension (36% of patients
    • Placental abruption
    • Spontaneous abortion
    • Preterm birth
    • Postpartum hemorrhage
slide28

Thyroid replacement and medications

  • Drugs that interfere with absorption:
    • Prenatal vitamins
    • Iron replacement
    • Antacids
    • Cholestyramine
  • Drugs that interfere with metabolism
    • Phenytoin
    • Rifampin
    • Carbamazapine
back to case29
Back to case
  • Increase her medication to 100 mcg per day to get her TSH <2.5 before conception
  • Once she becomes pregnant, check her TSH and adjust the dose as necessary
  • Monitor q trimester during pregnancy
slide30

Sub clinical hypothyroidism

  • Elevated TSH with ~normal FT4 and FT3
  • Prevalence 4-8.5%
  • Pregnant women 2-5%
  • Normal TSH 0.3 and 2.5 mU/L
    • Levels between 2.5 and 4.0 “gray zone”
    • Values >4.0 indicative of early thyroid failure
  • Treat?
    • controversial
postpartum thyroiditis
Postpartum Thyroiditis
  • Occurs in 5-10% of women
  • 25% of patients with DMI
slide32
Occurs 6-12 weeks postpartum
  • Phases
    • Hyperthyroid - last 1-2 months
    • Hypothyroid - last 6-9 months
  • Postpartum depression
    • Screen with a TSH as may be cause
treatment33
Treatment
  • Hyperthyroid phase
    • Anti-thyroid medications not effective
    • Beta blockers for symptoms
  • Hypothyroid phase
    • Treat with replacement for 6-12 months and then reduce or discontinue dose and recheck TSH in 6 weeks
thyroid nodules and cancer during pregnancy
Thyroid nodules and cancer during pregnancy
  • Increase in the prevalence of thyroid nodule during pregnancy
  • Increase in the growth of existing nodules during pregnancy
  • No evidence to suggest thyroid cancer arises de novo more frequently during pregnancy
evaluation
Evaluation
  • Lab evaluation of thyroid function
  • Ultrasound
  • FNA
  • Benign cytology - observe and follow postpartum
  • Malignant cytology - surgery recommended
slide37
Women with previously diagnosed or treated differentiated thyroid cancer require an increase in levothyroxine dosage during pregnancy
  • TSH of 0.1-0.8 mU/L for papillary or follicular cancer
  • TSH of <2.5 mU/L for patients with medullary thyroid cancer
summary
Summary
  • Normal physiology of pregnancy is such that the TSH will decrease in the first trimester due to similarities to HCG
    • If initially low, repeat second trimester and check FT4 and FT3
  • Hyperthyroidism - treat to maintain FT4 in the higher range of normal
  • Hypothyroidism - goal TSH 0.5 to 2.5 mU/L
reference
Reference
  • Casey B, Leveno K. Thyroid disease in pregnancy. Obstetrics and Gynecology 2006; 108 (5): 1283-1292
  • Hypothyroidism in the pregnant woman. Drug and therapeutic bulletin 2005; 44 (7): 53-55
  • LeBeau S, Mandel S. Thyroid disorders during pregnancy. Endocrinology and Metabolism Clinics of North America. 2006; 35: 117-136
  • Molitch M. Endocrine disease in pregnancy. Principles and Practice of Endocrinology and Metabolism 3rd edition.