This document discusses thyroid function tests and thyroid physiology during pregnancy. It provides normal ranges for various thyroid markers like TSH, T4, and T3 in pregnancy. It explains that human chorionic gonadotropin (hCG) secreted during pregnancy can stimulate the thyroid and cause a transient decrease in TSH in early pregnancy. Estrogen also increases thyroid-binding globulin levels, decreasing free thyroid levels but increasing total levels. The document recommends screening all pregnant women with TSH and free T4 tests and checking thyroid antibodies if levels are abnormal based on pregnancy-specific reference ranges.

1. Interpretation of
Thyroid function tests in
Pregnancy
DR. JYOTI BHASKAR
DR. SHARDA JAIN
DR. JYOTI AGARWAL

3. NORMAL THYROID PHYSIOLOGY

4. NORMAL THYROID PHYSIOLOGY

5. Hypothyroidism
Hyperthyroidism
Diseases of Thyroid Gland

6. Elevated TSH
(>4.5 mU/L
hypothyroidism
Low TSH (<4.5
mU/L
hyperthyroidism
Normal range: 0.5 –
4.5mU/L
One of the best thyroid function screening
test
TSH : Thyroid – Stimulation Hormone

7. Hypothyroidism
• Decreased T4
Hyperthyroidism
• Increased T4
Normal range: 65 –
150nmol/L
T4 : Serum Total Thyroxine

8. Hypothyroidism
• Decreased T3
Hyperthyroidism
• Increased T3
Normal range: 1.8 –
3nmol/L
T3: Serum Total Triiodothyronine

9. 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, 2006:1-13
http://www.aace.com/pub/pdf/guidelines/hypo_hyper.pdf.
T3/T4

10. Patterns of thyroid function tests during
assessment of thyroid function
Source: UpToDate.com.
Serum TSH Serum Free T4 Serum T3 Assessment
Normal hypothalamic-pituitary function
Normal Normal Normal Euthyroid
High Low Normal or low Primary hypothyroidism
High Normal Normal Subclinical hypothyroidism
Low High or normal High Hyperthyroidism
Low Normal Normal Subclinical hyperthyroidism
Abnormal hypothalamic-pituitary function
Normal 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.

11. 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

14. 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 gonadotropin
TSH: Thyroid stimulating hormone
TH: Thyroid hormone
TBG: Thyroxine-binding globulin

15. 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
hCG
TSH
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)
TBG
Total 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 T4
Free T3
Weeks of gestation
A
B C
TBG: Thyroxine- binding globulin
TSH: Thyroid stimulating hormone
HCG: Human chorionic gonadotropin
TT4: Total thyroxine
FT3: Free triiodothyronine
FT4: Free thyroxine

16. Thyroid evaluation in normal pregnancy
Recommendation Indication
TSH and FT4
Screening
Interpretation 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

17. Thyroid hormone changes
during pregnancy
First trimester
Second
trimester
Third
trimester
TSH
Normal or
decreased
Normal Normal
Free T4 Normal Normal Normal
Free T3 Normal Normal Normal
Total T4 High High High
Total T3 High High High

18. 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

19. What are the Screening tests to be done?
TSH
f T4 and anti TPO
IF HIGH ( Pregnancy specific levels)

20. Anti TPO
 Over 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.

21. 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

22. Anti TPO to be done
 Personal history of Thyroid or AI
disorders
 Family History of Thyroid disease
 Women with Goitre
 Women with history of miscarriage or
Preterm delivery
 Women with Type 1 diabetes

23. 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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