Thyroid Disease in Pregnancy

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Thyroid Disease in Pregnancy

• District 1 ACOG Medical Student Teaching Module
  2009

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Physiologic Changes in Thyroid Function During
Pregnancy

• Thyroid binding globulin (TBG) increases due to
  reduced hepatic clearance and estrogenic
  stimulation of TBG synthesis
• The test results that change in pregnancy are
  influenced by changes in TBG concentration
• Plasma iodide levels decrease due to fetal iodide
  use and increased maternal clearance -gt leads to
  notable increase in gland size in 15 of women
  (without abnormal TFTs)

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Physiologic Changes in Thyroid Function During
Pregnancy
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The Fetal Thyroid

• Begins concentrating iodine at 10-12 weeks
• Controlled by pituitary TSH by approximately 20
  weeks

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Hyperthyroidism

• Occurs in 0.2 of pregnancies Graves disease
  accounts for 95 of cases

Look for Nervousness tremor Tachycardia frequent
stools sweating heat intolerance weight
loss Goiter Insomnia Palpitations Hypertension lid
lag/lid retraction pretibial myxedema
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Fetal Neonatal Effects of Hyperthyroidism

• Associated with preterm delivery, low birth
  weight, fetal loss
• Fetal thyrotoxicosis (related to disease itself
  or treatment)
• Risk of immune-mediated hypo/hyperthyroidism (due
  to antibodies crossing the placenta, esp. in
  Graves or chronic autoimmune thyroiditis)
• Antibodies in Graves disease can be either
  stimulatory or inhibitory
• Neonates of women with Graves who have been
  surgically/radioactively treated are at higher
  risk, b/c not taking suppression

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Causes Diagnosis of Hyperthyroidism

• Most common cause of hyperthyroidism is Graves
  disease
• Document elevated FT4 or elevated FTI with
  suppressed TSH, in absence of goiter/mass
• Most patients have antibodies to TSH receptor,
  antimicrosomal, or antithyroid peroxidase
  antibodies, but measurement of these is not
  required (though some endocrinologists recommend
  measuring TSI, which are stimulatory antibodies
  to TSH receptor)
• Other causes
• Excess TSH production, gestational trophoplastic
  disease, hyperfunctioning thyroid adenoma, toxic
  goiter, subacute thyroiditis, extrathyroid source
  of TH

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Treatment of Hyperthyroidism

• Goal is to maintain FT4/FTI in high normal range
  using lowest possible dose (minimize fetal
  exposure)
• Measure FT4/FTI q2-4 weeks and titrate
• Thioamides (PTU/methimazole) -gt decrease thyroid
  hormone synthesis by blocking organification of
  iodide
• PTU also reduces T4-gtT3 and may work more quickly
• PTU traditionally preferred (older studies found
  that methimazole crossed placenta more readily
  and was associated with fetal aplasia cutis
  newer studies refute this)

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Treatment of Hyperthyroidism

• Effect of treatment on fetal thyroid function
• Possible transient suppression of thyroid
  function
• Fetal goiter associated with Graves (usually
  drug-induced fetal hypothyroidism)
• Fetal thyrotoxicosis due to maternal antibodies
  is rare -gt screen for growth and normal FHR
• Neonate at risk for thyroid dysfunction notify
  pediatrician
• Breastfeeding safe when taking PTU/methimazole

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Treatment of Hyperthyroidism

• Beta-blockers can be used for symptomatic relief
  (usually propanolol)
• Reserve thyroidectomy for women in whom thioamide
  treatment unsuccessful
• Iodine 131 contraindicated (risk of fetal thyroid
  ablation especially if exposed after 10 weeks)
  avoid pregnancy/breastfeeding for 4 months after
  radioactive ablation

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Hypothyroidism

• Symptoms fatigue, constipation, cold
  intolerance, muscle cramps, hair loss, dry skin,
  slow reflexes, weight gain, intellectual
  slowness, voice changes, insomnia
• Can progress to myxedema and coma
• Subclinical hypothyroidism elevated TSH, normal
  FTI in asymptomatic patient
• Associated with other autoimmune disorders
• type 1 DM -gt 5-8 risk of hypothyroidism 25
  postpartum thyroid dysfunction

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Hypothyroidism Fetal Neonatal Effects

• Higher incidence of LBW (due to medically
  indicated preterm delivery, PEC, abruption)
• Iodine deficient hypothyroidism -gt congenital
  cretinism (growth failure, mental retardation,
  other neuropsychologic deficits)

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Causes Diagnosis of Hypothyroidism

• Causes
• Hashimotos (chronic thyroiditis most common in
  developed countries) iodine deficiency -gt both
  associated with goiter
• Subacute thyroiditis -gt not associated with
  goiter
• Thyroidectomy, radioactive iodine treatment
• Iodine deficiency (most common worldwide rare in
  US)

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Treatment of Hypothyroidism

• Treat with levothyroxine in sufficient dose to
  return TSH to normal
• Adjust dosage every 4 weeks
• Check TSH every trimester