Pregnancy and the thyroid gland: Important issues for mom and baby - - PowerPoint PPT Presentation

Pregnancy and the thyroid gland:

Important issues for mom and baby

TRH TRH TSH TSH

PITUITARY PITUITARY Thyroid Thyroid

Normal Function : Normal Function : Hypothalamic

Hypothalamic-

• Pituitary

Pituitary-

• Thyroid Axis is Centrally Determined

Thyroid Axis is Centrally Determined

HYPOTHALAMUS HYPOTHALAMUS

Thyroxine (T4)

( - ) Classic negative feedback loop

T4 T4 T3 ( - )

T3

The Thyroid Gland

• 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

• 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

• Type 1 not modified
• Type 2 (placenta) maintains T3 production locally
• Type 3 (placenta)
• (protective mechanisms)

TRH TRH TSH TSH

PITUITARY PITUITARY Thyroid Thyroid

Normal Function : Normal Function : Hypothalamic

Hypothalamic-

• Pituitary

Pituitary-

• Thyroid Axis is Centrally Determined

Thyroid Axis is Centrally Determined

HYPOTHALAMUS HYPOTHALAMUS

Thyroxine (T4)

( - ) Classic negative feedback loop

T4 T4 T3 ( - )

T3 Placenta

HCG

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

– 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

– 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

• f 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:
• rder 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