3. EFFECTS OF PREGNANCY ON THYROID
PHYSIOLOGY
Physiologic Change Thyroid-Related Consequences
↑ Serum thyroxine-binding globulin ↑ Total T4 and T3; ↑ T4 production
↑ Plasma volume ↑ T4 and T3 pool size; ↑ T4
production; ↑ cardiac output
First trimester ↑ in hCG ↑ Free T4; ↓ basal thyrotropin; ↑ T4
production
↑ Renal I- clearance ↑ Iodine requirements
↑ T4 production; fetal T4 synthesis during
second and third trimesters
↑ Oxygen consumption by fetoplacental
unit, gravid uterus, and mother
↑ Basal metabolic rate; ↑ cardiac
output
4. Changes in Thyroid Function
Maternal
Status
TSH
**initial
screening
test**
Free T4 Total T4 Total T3
Pregnancy Decrease No
change
Increase Increase
Hyperthyroidism Decrease Increase Increase Increase or
no change
Hypothyroidism Increase Decrease Decrease Decrease
or no
change
5. HYPOTHYROIDISM
The prevalence of hypothyroidism in India is 13.13%,
when ULRR of TSH is set at 4.5mIU/L, however this percentage
increases upto 36.07% when ULRR is set at trimester specific
reference range as suggested by ATA
Normal TSH level in non-pregnant female- 0.5-4.5
mIU/L
Endemic iodine deficiency is the most common cause
of hypothyroidism seen in pregnant women worldwide
IJEM,year:2016,volume:20,issue:3,page:387-390
6. Primary Hypothyroidism
Developed Countries
Hashimoto’s thyroiditis – Chronic thyroiditis
prone to develop postpartum thyroiditis.
Worldwide
Iodine deficiency
Other Causes:
Subacute thyroiditis -> not associated with goiter
Thyroidectomy, radioactive iodine treatment
7. Hashimoto’s Thyroiditis
An inflammatory disorder of thyroid glands
More common in those with other autoimmune
diseases
Almost 100% associated with anti-TPO antibody
May cause transient hyperthyroidism
8. Iodine Deficiency
Affect 38% of worldwide population
Sources of iodine: Iodized salt and seafood cow milk, egg,
beans
Congenital cretinism (growth failure, mental retardation,
other neuropsychological deficits)
Recommended Average intake in pregnancy & lactation-
250 µg/d
American Thyroid Association 2017 Guidelines
10. Subclinical Hypothyroidism
Elevated TSH (> 4.5 mIU/l) with normal FT4, FT3
More common in women with autoimmune diseases
50 % hypothyroidism in 8 years
May cause decrease in IQ
American Thyroid Association 2017 Guidelines
11. Symptoms of Hypothyroidism
Slowing of metabolic processes:
Lethargy/fatigue weight gain cognitive dysfunction
cold intolerance constipation bradycardia
delayed relaxation of tendon reflexes
slow movement and slow speech
Deposition of matrix substances:
Dry skin hoarseness edema
puffy face and eyebrow loss peri-orbital edema
enlargement of the tongue
Others
Decreased hearing myalgia and paresthesia depression
menorrhagia arthralgia pubertal delay
galactorrhea
14. Pregnancy and fetal outcomes in hypothyroidism
High fetal wastage, in form of abortion , stillbirths and pre-
maturity
Deficient intellectual development of child
Pre-eclampsia
Anemia
Still births
Abruptio Placenta
Post partum haemorrhage
LBW babies
15. Serum TSH During Pregnancy
Trimester-specific reference ranges for TSH, as defined
in populations with optimal iodine intake, should be
applied
If trimester-specific reference ranges for TSH are not
available in the laboratory, the following reference
ranges are recommend:
1st trimester 0.1-2.5 mIU/L;
2nd trimester 0.2-3.0 mIU/L;
3rd trimester 0.3-3.0 mIU/L
American Thyroid Association Guidelines 2011
16.
17. 2017 Guidelines of the American Thyroid
Association
According to new guidelines, the upper limit of reference
range of TSH during First Trimester to be set at 4mIU/L and
for 2nd & 3rd trimester is same as general population
The recommendation is to first look at the population
specific information, then to use the 4mIU/L upper limit if
that is not available
30. Maternal thyroid dysfunction during pregnancy may affect
maternal health, fetal health, and obstetric outcome
During early gestation, TSH is suppressed by 20% to 50%
by week 10 due to the steep increase in hCG concentrations,
resulting from increased hCG-induced thyroidal secretion
of T 4 and T 3
Therefore, maternal serum TSH does not provide a good
indicator for the control of thyroid dysfunction in the first
trimester unless trimester specific ranges are available
31. TSH levels may be misleading in the first trimester and T 4
values either total or free will give a more accurate estimate
of clinical status
Later in gestation, TSH levels are reliable, whereas T 4 may
fall especially in the third trimester but this does not
indicate hypothyroidism
TPO antibodies can predict the risk of hypothyroidism in
later life
32.
33. Treatment of Hypothyroidism
American Thyroid Association and American Association
of Clinical Endocrinologist 2011 recommended
replacement therapy beginning with Levothyroxine in dose
of :
1-2mcg/kg/day or approx 100mcg/day
Adjust dosage every 4 weeks
Thyroxine dose is adjusted by 25-50 mcg increments until
TSH values become normal
34. Why is iodine requirement increased during
pregnancy?
• During pregnancy, demand for iodine is increased
by approximately 50%
• This is due to:
Increased maternal thyroid hormone synthesis
Enhanced urinary iodine excretion
Utilization of iodine by the fetus
35. Should all pregnant women be screened for
thyroid dysfunction?
Ideally all pregnant women should be screened for
thyroid dysfunction during the first trimester
ACOG recommends screening of all pregnant women
36. What is the best screening test for evaluation of
thyroid dysfunction during pregnancy?
Measurement of serum TSH is the best screening test
for evaluation of thyroid dysfunction during pregnancy
However, levels of TSH should be interpreted according
to trimester-specific range
If serum TSH is out of reference range for pregnancy,
then estimation of free T 4 /total T 4 should be
performed
37. How to define subclinical and overt
hypothyroidism during pregnancy?
Those with TSH values above the trimester-specific
reference range with normal free T 4 are diagnosed to have
subclinical hypothyroidism
Those with TSH value above the reference range but <10
mIU/ml with a low free T 4 or TSH >10 mIU/ml
irrespective of free T 4 level are considered to have overt
hypothyroidism during pregnancy
38. What are the risks associated with subclinical
hypothyroidism during pregnancy?
Maternal risks associated with subclinical
hypothyroidism are miscarriage, preterm delivery, and
stillbirths, whereas fetal risks include low birth weight
and possibly impaired neurocognitive development
39. Is treatment recommended for all women with
subclinical hypothyroidism during pregnancy?
Yes
Treatment of subclinical hypothyroidism during
pregnancy is associated with favorable maternal
outcome
However, the effect of maternal subclinical
hypothyroidism on fetal neurocognitive development is
not so clear
40. What should be the TSH target in a hypothyroid
woman planning pregnancy?
The recommended TSH level in a nonpregnant individual
with hypothyroidism is 0.4–4.5 mIU/ml
However, when a woman is planning pregnancy, TSH
should be targeted <2.5 mIU/ml as TSH even in the upper
normal range (2.5–4.5 mIU/ml) is considered as relative
hypothyroidism for a pregnant female during first
trimester
41. Patients receiving therapy for overt/subclinical
hypothyroidism prior to conception should be advised
to increase the dose of levothyroxine by 30–50% at4–6
weeks of gestation
TSH between 5–10 mIU/l, increment of levothyroxine
by 25–50 μg/day
TSH 10–20 mIU/l, increment by 50–75 μg/day
TSH >20 mIU/l, increment by 75–100 μg /day
42. A 26-year-old lady, who is a known hypothyroid
for 5 years, on levothyroxine 50 μg per day
presented at 12 weeks of gestation with a TSH of
13 mIU/ml. How to optimize the therapy?
43. In this case the dose of levothyroxine was increased to
125 μg/day
She was advised to take iron and calcium supplements
6–8 h after intake of levothyroxine as they interfere
with the absorption of levothyroxine
Her repeat TSH after 4 weeks was 1.2 mIU/l
44. A 33 year-old G3 P2 at 10 weeks GA comes to the office for her 1st
antenatal visit. She reports that she had hypothyroidism in the
distant past, but was never treated and is asymptomatic. Physical
examination is normal. On bimanual examination her uterus is 10
weeks size and FHR is 150 bpm. Her TSH level is 13.1 and, free T4
level is 0.7, with raised anti T.P.O. levels.
Should the anti-thyroid peroxidase antibody levels be done in
such patients,how does a raised anti TPO affect the treatment or
pregnancy outcome.
Which of the following would be done next-
A) Begin levothyroxine
B) Repeat serum TSH and Free T4 after 20 weeks of gestation
C) Measure serum thyroid-stimulating immunoglobulins
D) Perform ultrasonography of the maternal thyroid
45. A 33 year-old G3 P2 at 10 weeks GA comes to the office for her 1st
antenatal visit. She reports that she had hypothyroidism in the
distant past, but was never treated and is asymptomatic. Physical
examination is normal. On bimanual examination her uterus is 10
weeks size and FHR is 150 bpm. Her TSH level is 13.1 and, free T4
level is 0.7, with raised anti T.P.O. levels.
Should the anti-thyroid peroxidase antibody levels be done in
such patients,how does a raised anti TPO affect the treatment or
pregnancy outcome.
Which of the following would be done next-
A) Begin levothyroxine
B) Repeat serum TSH and Free T4 after 20 weeks of gestation
C) Measure serum thyroid-stimulating immunoglobulins
D) Perform ultrasonography of the maternal thyroid
46. Although the patient is asymptomatic she has laboratory
evidence of overt hypothyroidism with an elevated TSH and
low free T4 level
She also has elevated anti-thyroid peroxidase antibody level
which indicates that the likely cause of her hypothyroidism is
chronic autoimmune thyroditis (Hashimoto’s disease)
The anti-thyroid peroxidase antibodies also indicate an
increased risk of her developing other autoimmune disease,
such as adrenal insufficiency or type 1 DM
Hypothyroidism in pregnancy has been associated with pre-
eclampsia, GHTN, abruptio placentae, preterm delivery, and
neuropsychologic deficits in the child
