interpretation of thyroid function tests in pregnancy, jyoti bhaskar , dr. sharda jain, dr. jyoti...
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Interpretation of Thyroid function
tests in PregnancyDR. JYOTI BHASKARDR. SHARDA JAINDR. JYOTI AGARWAL
NORMAL THYROID PHYSIOLOGY
NORMAL THYROID PHYSIOLOGY
Hypothyroidism Hyperthyroidism
Diseases of Thyroid Gland
Elevated TSH (>4.5 mU/Lhypothyroidism
Low TSH (<4.5 mU/Lhyperthyroidism
Normal range: 0.5 – 4.5mU/L
One of the best thyroid function screening test
TSH : Thyroid – Stimulation Hormone
Hypothyroidism• Decreased T4
Hyperthyroidism• Increased T4
Normal range: 65 – 150nmol/L
T4 : Serum Total Thyroxine
Hypothyroidism• Decreased T3
Hyperthyroidism• Increased T3
Normal range: 1.8 – 3nmol/L
T3: Serum Total Triiodothyronine
Laboratory Diagnosis TSH assay: Primary test
to establish the diagnosis
Additional tests: Estimation of free T3
and T4 Test for thyroid
autoantibodies Thyroid
scan/ultrasonography Serum cholesterol-
in hypothyroidism
T3/T4
Subclinical hypothyroidism
Overt hypothyroidism
TSH
TSH
AACE medical guidelines for clinical practice for the evaluation and treatment of hyperthyroidism and hypothyroidism, 2006:1-13http://www.aace.com/pub/pdf/guidelines/hypo_hyper.pdf.
T3/T4
Patterns of thyroid function tests during assessment of thyroid function
Source: UpToDate.com.
Serum TSH Serum Free T4 Serum T3 AssessmentNormal hypothalamic-pituitary functionNormal Normal Normal EuthyroidHigh Low Normal or low Primary hypothyroidismHigh Normal Normal Subclinical hypothyroidismLow High or normal High HyperthyroidismLow Normal Normal Subclinical hyperthyroidismAbnormal hypothalamic-pituitary functionNormal or high High High TSH-mediated hyperthyroidism
Normal or low* Low or low-normal Low or normal Central hypothyroidism
* In central hypothyroidism, serum TSH may be low, normal or slightly high.
Antithyroid peroxidase antibodies
Used to diagnose suspected Hashimoto’s thyroiditis in
hypothyroidism
Antithyroglobulin antibodies
Used to diagnose autoimmune thyroiditis or
Graves’ disease in hyperthyroidism
Thyroid Antibodies
Thyroid Physiology in Pregnancy
Decreased TSH
Placenta hCG
Increased TH degradation
Thyroid stimulation for increased TH
Production
Estrogen
Increased serum TBG
Increased hepatic production of TBG
Increased half life of TBG
Type 3 deiodinase
Stimulates TSH receptor
Decreased free TH
Stimulation of hypothalamic pituitary axisIncreased serum TH
hCG: Human chorionic gonadotropinTSH: Thyroid stimulating hormoneTH: Thyroid hormoneTBG: Thyroxine-binding globulin
Increased oestrogen in pregnancy
Two- to threefold
increase in TBG
Decrease Free T3 and T4
Similar structure of hCG and TSH
hCG stimulates
release of T3 and T4
Transient TSH decrease in
weeks 8 to 14
Increased peripheral
metabolism of T3 and T4
Decrease Free T3 and T4
Thyroid Physiology in Pregnancy
1. Jameson JL. Harrison's Principles of Internal Medicine. 2008:2224-2247.2. Lazarus JH. Br Med Bull.2010;1-12.3. Galofre JC, Davies TF. J Womens Health (Larchmt). 2009;18(11):1847-1856..
0
50
75
100
125
150
0
0.5
1.5
2.5
3.5
4.5
40 8 12 16 20 24 28 32 36 40
TSH
(mU
/L)
hCG
(IU
/mL
hCGTSH
Weeks of gestation
0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
40 8 12 16 20 24 28 32 36 40
TT4
(mcg
/dL)
TBG
(mg/
dL)
TBGTotal T4
Weeks of gestation
0.2
0.6
1.0
1.4
1.8
160
220
280
340
400
40 8 12 16 20 24 28 32 36 40
FT3
(pg/
dL)
FT4
(ng/
dL)
Free T4Free T3
Weeks of gestation
A
B CTBG: Thyroxine- binding globulinTSH: Thyroid stimulating hormoneHCG: Human chorionic gonadotropinTT4: Total thyroxineFT3: Free triiodothyronineFT4: Free thyroxine
Thyroid evaluation in normal pregnancy
Recommendation Indication
TSH and FT4 ScreeningInterpretation should be trimester specific
TPO-Ab and Tg-Ab Presence of AITD
Ultrasound Advisable when nodular disease is suggested by clinical examination
1. Galofre JC, Davies TF. J Womens Health (Larchmt). 2009;18(11):1847-1856.
Usual recommendations for thyroid evaluation in normal pregnancy
Thyroid hormone changes during pregnancy
First trimester Second trimester
Third trimester
TSH Normal or decreased Normal Normal
Free T4 Normal Normal NormalFree T3 Normal Normal NormalTotal T4 High High HighTotal T3 High High High
What is a normal TSH level in pregnancy?
Reference range used for
nonpregnant population
First trimester Second trimester
Third trimester
FT4 (pmol/L)
9–26 (0.7–2.02 ng/dL)
10–16 (0.78–1.25 ng/dL)
9–15.5 (0.70–1.3 ng/dL)
8–14.5 (0.62–1.13 ng/dL)
FT3 (pmol/L)
2.60–5.7(0.2–0.44 ng/dL)
3–7 (0.23–0.55 ng/dL)
3–5.5(0.23–0.43 ng/dL)
2.5–5.5(0.2–0.43 ng/dL)
TSH (mu/L) 0.3–4.2 0.1–2.5 0.2–3.0 0.3–3.0
What are the Screening tests to be done?
TSH
f T4 and anti TPO
IF HIGH ( Pregnancy specific levels)
Anti TPOOver 58% of cases of SCH have anti
TPO
It is Positive only when levels are TWO times the Normal
Once positive – should not be repeated again.
Anti TPO Significance :
1. It defines the cause as Autoimmune 2. It cautions for increased chances of
PPT 3. Normal TSH with positive antibodies
are prone to become hypothyroid – Need Monitoring
Anti TPO to be done
Personal history of Thyroid or AI disorders
Family History of Thyroid diseaseWomen with GoitreWomen with history of
miscarriage or Preterm deliveryWomen with Type 1 diabetes
TAKE HOME MESSAGE
We need to understand the thyroid physiology in pregnancy before interpreting the results.
All pregnant women have to be screened for Thyroid disorders at the first antenatal visit
The screening test recommended is TSH
Other two tests that are of clinical significance are
Free T4 and Anti TPO
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