Download Pregnancy and the thyroid gland

Pregnancy and the thyroid
gland:
Important issues for mom and
baby
Normal Function : Hypothalamic-PituitaryThyroid Axis is Centrally Determined
T4
T3 ( - )
HYPOTHALAMUS
TRH
(- )
PITUITARY
Classic negative feedback loop
T4
TSH
Thyroid
Thyroxine (T4)
T3
The Thyroid Gland
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Shaped like a butterfly
Base of the neck
About 10-20 g in the adult
Starts functioning at about 11 weeks in the
fetus
• Most maternal T3 and T4 are inactivated
by the placenta but the small amount that
reaches the fetus is important for early
fetal brain development
What does T3 and T4 affect?
• Everything!
– O2 consumption, heat production, free radical
formation
– Cardiovascular
– Sympathetic
– Pulmonary
– Hemapoietic
– GI
– Skeletal
– Neuromuscular
– Lipids and Carbohydrates
– Metabolic turnover of many hormones
Thyroid Function in the Fetus
• Prior to development of independent fetal thyroid
function, fetus is dependent on maternal thyroid
hormones
• 11th week of gestation measurable TSH and
TRH are present in the fetus
• At this time the fetal thyroid begins to trap iodine
• Secretion of thyroid hormone begins 18-20
weeks
• At birth there is a marked rise in T4 and T3
Thyroid Function in Pregnancy
•
Rise in TBG (thyroid binding globulins)
– Effect of estrogen
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Rise in T4 and T3
– New equilibrium of free and bound T3 and
T4
•
hCG is weak TSH agonist
– Can cause thyroid enlargement
– And decreased TSH
Thyroid and Pregnancy
• Increased iodine clearance
– If low iodine intake can impair thyroid
hormone synthesis
• Maternal thyroid antibodies can affect the
fetal thyroid function
Maternal thyroid physiology
• First half of gestation to term
– Increase in thyroid binding globulin
– Lower free hormone concentrations of T3 and
T4
– Stimulation of hypothalamic-pituitary-thyroid
axis
– (protective mechanisms)
Maternal thyroid physiology
continued
• First trimester
– as hCG peaks and cross reacts with TSH
receptor: partial inhibition of pituitary and
lowering of TSH level between wks 8 and 14
– 20% of women will have TSH dip below lower
level of normal: these women will have higher
hCG concentrations
– In normal pregnancies these are of minor
consequence
Maternal thyroid physiology
continued
• Throughout pregnancy
– Alterations in the peripheral metabolism of
thyroid hormone more prominent in second
half
– Three enzymes deiodinate thyroid hormones
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Type 1 not modified
Type 2 (placenta) maintains T3 production locally
Type 3 (placenta)
(protective mechanisms)
Normal Function : Hypothalamic-PituitaryThyroid Axis is Centrally Determined
T4
T3 ( - )
HYPOTHALAMUS
TRH
(- )
PITUITARY
Classic negative feedback loop
T4
TSH
HCG
Placenta
Thyroid
Thyroxine (T4)
T3
Iodine deficiency
• Iodine deficiency: controversial.
No recommendations for US women yet but
as providers we should instruct our
patients that iodine in the diet is
recommended.
Thyroid Diseases in Pregnancy
• Autoimmune thyroid disease
– Hyperthyroidism 0.2%
– Hypothyroidism
• Clinical 0.3%
• Subclinical 2-3%
Thyroid Diseases in Pregnancy
continued
• Non Autoimmune
– Gestational Hyperthyroidism 5-10% (↑ HCG)
– Iodine deficiency ?
– Goiter ?
– Post ablation (cancer, goiter) ?
Laboratory evaluation of thyroid
function during pregnancy
• TSH (ORDER THIS ONE!)
– If low, repeat with a T4
– If higher than normal value repeat and consult
• Remember that total T4 and total T3 can
be elevated because of increased
thyroxine-binding globulin
• Anti-thyroid antibodies
• Drugs and thyroid function
• Nonthyroidal illness and thyroid function
Thyroid Dysfunction and
reproductive disorders
• Hyperthyroidism
– Increased SAB’s
– Possible low birth weight
– Possible neonatal goiter in Graves (TSI)
• Hypothyroidism
– Increased SAB’s
– Possible effects of anti-TPO
• Radioiodine and gonadal function
Hyperthyroidism and Pregnancy
• Signs and symptoms
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Heat intolerance
Sweating
Fatigue
Anxiety
Emotional lability
Tachycardia, pounding heart, palpitations
Weight loss
Nausea/excessive vomiting
Diarrhea
CHF, myopathy, lymphadenopathy
Hyperthyroidism continued
• TSH and T4 most important labs
• Other considerations:
liver enzymes, CBC, alk phos, serum
calcium, thyroid antibodies
Differential diagnosis
• Hyperthyroidism in pregnancy
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Graves (90-95%)
Toxic adenoma
Toxic multinodular goiter
Hyperemesis gravidarum
Gestational trophoblastic disease
Exogenous T4 and T3
De Quervain (subacute) thyroiditis
Painless lymphocytic thyroiditis
• Extremely rare
– Struma ovarii
– TSH-producing pituitary tumor
– Metastatic follicular cell carcinoma
Hyperthyroidism continued
• Treatment
– Thionamide therapy (methimazole or PTU)
• In United States PTU is most often used
• Infant should have ultrasound for signs of hypothyroidism
– Beta blockers
• Propranolol/Atenolol for tachycardia or tremulousness
(need to watch fetus for bradycardia, etc)
– Iodides – rarely used now
– Surgery – rarely needed
• Thyroid storm –
– severe hyperthyroidism with mental status changes,
fever and/or CV collapse
Fetal and Neonatal hyperthyroidism
Usually produced by transplacental passage
of thyroid stimulating immunoglobulins in
Graves disease (TSI)
Antibodies can continue to be present after
ablation, surgery and even in Hashimoto’s
thyroiditis
Watch for TSI in mom of >300% as this can
be predictive of fetal hyperthyroidism
Hypothyroidism
• Most common cause is chronic
autoimmune thyroiditis – Hashimoto’s
(with or without goiter)
• Ask if there is a family h/o thyroid
problems
• If goiter and/or family h/o thyroid disease:
order a TSH and anti-TPO.
Hypothyroidism
• If known hypothyroidism and patient is on
replacement therapy:
– Ask pt to get TSH as soon as she knows
she’s pregnant AND
– Take one extra thyroid pill that day
– Consult
• She will likely need 30% more Thyroxine
in first trimester
Hypothyroidism
• TSH goal is 0.2 to 2.0 during pregnancy
– ‘normal’ is 0.2 – 5.5 on most assays
• Labs every four weeks during pregnancy
• Dose of thyroxine can vary depending on
the cause of hypothyroidism
• If hypothyroid because of thyroidectomy
for thyroid cancer: refer pt to
endocrinologist
Conclusions
• Many changes in maternal thyroid function
• Know if your patient has thyroid problems
before conception IF POSSIBLE
– Pre-pregnancy counseling
• Women who have thyroid problems by
history will need close monitoring
• If you have questions: ask