thyroid function in pregnancy & post-partum thyroid hormone synthesis increases by 30 - 50% in...
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Thyroid function in
Pregnancy & Post-Partum
Dr Simon ForehanEndocrinologist
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Outline
• Thyroid physiology
• Adaptations in pregnancy & Iodine
• Thyroid dysfunction
• Pregnancy
• Hyperthyroidism
• Hypothyroidism
• Post-partum
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• Marked changes to thyroid physiology in pregnancy
• Thyroid disease affects women of child bearing age
• Common
• Up to 3% have abnormal thyroid function
• Thyroid auto-antibodies are found in 5-15% of women
• Implications for mother and baby
• Treatable
Background
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THYROID PHYSIOLOGY
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TSH
T4 T3
Iodine
pituitary
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TSH
T4 T3
pituitary
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TSH
T4 T3
pituitary
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TSH
T4 T3
pituitary
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TSH
T4 T3
pituitary
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TSH
T4 T3
pituitary
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TSH
T4 T3
pituitary
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Thyroid function & Iodine metabolism in
pregnancy
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TSH
T4 T3
Iodine
pituitary
T4 T3
Placenta
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• Increased demand
• Increased plasma volume
• TBG – pool increased
• Renal clearance
• Feto-placental unit uptake
• Placental deiodination
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i. Normal thyroid hormone synthesis increases by 30-50% in pregnacy
ii. Iodine requirements are increased in pregnancy
• RDI in pregnancy 250µµµµg/day
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Reference ranges & normal function in
pregnancy
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TSH
T4 T3
pituitary
HCG
Pregnancy
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TSH
T4 T3
pituitary
HCG
Pregnancy
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TSH
T4 T3
pituitary
HCG
Pregnancy
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TSH
T4 T3
pituitary
HCG
Pregnancy
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HCG
TSH
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i. Predictable changes to thyroid function in pregnancy
ii. Trimester specific reference ranges
iii. Use of non-pregnant ranges may:
i. Under call hypofunction
ii. Over call hyperfunction
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Hypothyroidism
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Hypothyroidism
TSH
T4 T3
pituitary
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Hypothyroidism
TSH
T4 T3
pituitary
•Intolerance of cold
•Headache
•Constipation
•Weight gain
•Lethargy
•dry skin
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Hypothyoidism - spectrum
• Overt
• Low fT4, high TSH
• Subclinical
• Normal fT4, high TSH
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5%
19%
0 5 10 15 20 25
Fetal Brain Development
• Children of women with untreated
hypothyroidism during pregnancy:
– Averaged 7 points lower on IQ testing*
– Had a significant percentage (19%) of IQ ≤≤≤≤85
IQ Scores of ≤≤≤≤85
Control
Children
Children of Mothers with
Untreated Hypothyroidism(P<0.005)
*Full-scale Wechsler Intelligence Scale for Children.
Haddow JE, et al. N Engl J Med. 1999;341:549-555.
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• Women with thyroid autoimmunity and who are euthyroid in the early stages of pregnancy are at risk of developing hypothyroidism later; therefore, their serum TSH levels should be monitored.
• If overt hypothyroidism is diagnosed during pregnancy, thyroid function tests should be normalized as rapidly as possible.
• Known hypothyroidism need dose increase 30-50%, earlier increase in assisted reproduction (due to oestrogen effect on TBG)
Thyroid hormone replacement
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Hyperthyroidism
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Hyperthyroidism
TSH
T4 T3
pituitary
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Hyperthyroidism
TSH
T4 T3
pituitary
•Palpitations
•Sweats
•Flushing
•Anxiety
•Intolerance of hot
•Headache
•Tremor
•Diarrhoea
•Weight loss
•Lethargy
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Pregnancy induced hyperthyroidism
• Transient ‘gestational
thyrotoxicosis’
• hCG mediated
• 2-4% of pregnancies
• Hyperemesis Gravidarum (HG)
associated with hyperthyroidismTSH
T4 T3
HCG
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Graves’ disease
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TSH
T4 T3
pituitary
TRAb
Graves’ disease
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TSH
T4 T3
pituitary
TRAb
Graves’ disease
T4 Placenta
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Graves’ disease in pregnancy
• Complicates 1 in 500 pregnancies
• Untreated hyperthyroidism causes
• Miscarriage
• premature labour
• low birthweight
• Pre-eclampsia
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Graves’ disease in pregnancy
• Transplacental passage of TSH rec. Ab can cause fetal and
neonatal thyrotoxicosis
• US to detect fetal tachycardia and goitre
• Effect of PTU treatment in lactating mothers
• Use as low doses as possible
• Take dose immediately after breast feeding
• Limited, if any effect on infants’ thyroid function
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Post partum thyroiditis• 5% of women (30-50% of the ~10% of women who have thyroid
peroxidase antibodies)
• rebound of immunocompetence after delivery
• Transient hyperthyroidism followed by hypothyroidism followed by recovery
• 25% develop permanent hypothyroidism
• Recurrent postpartum thyroiditis occurs in up to 80% of subsequent pregnancies
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i. Predictable changes to thyroid function in pregnancy
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i. Predictable changes to thyroid function in pregnancy
ii. Increased iodine requirements
• RDI 250mcg
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i. Predictable changes to thyroid function in pregnancy
ii. Increased iodine requirements
• RDI 250mcg
iii. Trimester specific reference ranges
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i. Predictable changes to thyroid function in pregnancy
ii. Increased iodine requirements
• RDI 250mcg
iii. Trimester specific reference ranges
iv. Thyroid dysfunction is important to recognise and is effectively treated
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i. Predictable changes to thyroid function in pregnancy
ii. Increased iodine requirements
• RDI 250mcg
iii. Trimester specific reference ranges
iv. Thyroid dysfunction is important to recognise and is effectively treated
v. In established hypothyroidism thyroxine needs to be increased
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i. Predictable changes to thyroid function in pregnancy
ii. Increased iodine requirements
• RDI 250mcg
iii. Trimester specific reference ranges
iv. Thyroid dysfunction is important to recognise and is effectively treated
v. In established hypothyroidism thyroxine needs to be increased
vi. High index of suspicion for post-partum thyroiditis
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Antenatal screening?
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WHO TO SCREEN?