3. • A 32 year old healthy woman presents for
evaluation following a missed menstrual cycle.
She believes she may be pregnant. She is feeling
well. Her medical history is notable for Graves’
hyperthyroidism, which was treated with
radioactive iodine ablation 2 years ago. She is
currently treated with LT4 and her most recent
TSH concentration 4 mo ago was normal.
4. • Testing confirms the patient is pregnant
and she is currently at 9 weeks’ gestation.
She has continued to take her LT4 daily
without any missed dose.
5. Questions
what is the most appropriate
recommendation ?
• A-The patient is likely euthyroid, and no intervention is
required.
• B- the patient is likely hypothyroid , and her LT4 dose
should be increased.
• C- The patient is likely hypothyroid, although no LT4
dose adjustment should be made because this represent
normal gestational physiology that will normalize.
• D- The patient is likely hyperthyroid and her dose of
LT4 should be decreased.
• E- The patient is likely hyperthyroid, although no LT4
dose adjustment should be made because this
represents normal gestational physiology which will
normalize.
6. comment
• On average, a 40% increase in maternal LT4 is required
during pregnancy to maintain euthyroidism. This
increased demand occurs early in pregnancy ,often
before the pregnancy is diagnosed.
• If the thyroid is functional, increased pituitary demand
stimulates thyroid hormone production seamlessly, and
no biochemical abnormality will occur.
• In patients with thyroid dysfunction (prior surgery, RAI
ablation, or Hashimoto’disease), the thyroid can not
adapt to pituitary stimulation and increased dose of
exogenous LT4 must be administered
7. • This patient has no functional thyroid tissue because of
prior RAI treatment. Although she was euthyroid prior
to conception, it is likely she is presently hypothyroid
and her LT4 dose must be increased to compensate for
greater demand. Normally, a 30%dose increase is
provided with repeat testing recommended in 2-4
weeks.
• If this patient had no history of thyroid disease, testing
at 9 weeks gestation would likely demonstrate an
euthyroid, or perhaps a mildly hyperthyroid (due to
hCG stimulation of the thyroid gland) biochemical state.
• Mild hyperthyroidism in the first trimester due to hCG
is physiologic and resolves spontaneously.
8. • The same patient now presents for a
follow up visit at 21 weeks’ gestation.
• She is feeling well.
• Her serum TSH on LT4 is 0.96mIU/L
9. QUESTATIONS
What additional testing should be performed ?
• A-No additional testing.
• B- Fetal TSH by cordocentesis.
• C- Maternal TRAb titer.
• D- Maternal FT4.
• E- Maternal TPO Ab titer.
10. comment
• In women with history of Graves’ disease who have
undergone RAI ablation or thyroidectomy TRAb may
still be present, and maternal thyroid function can not be
used as an index of Graves’ disease activity. Therefore,
maternal serum TRAb should be measured by 20-24
weeks’ gestation to help determine the risk for fetal and
neonatal hyperthyroidism.
• A TRAb level more than three times the upper limit of
normal is an indication for close follow up because risk
to the fetus is increased.
11. Comment 2
• Cordocentesis carries a risk of fetal loss and therefore is
only rarely used for testing fetal thyroid function.
• LT4 is dosed to normalize maternal TSH; measuring FT4
would not change management.
• The serum TPO Ab would likely be positive in the
setting of the history of Graves’ disease, but TPO Ab
testing would not be clinically used in this setting.
15. Case 2
a 29- year old patient present at 10 weeks’ gestation with
the following thyroid function tests: sTSH less than
0.01mIU/L, FT4 index 26 (trimester specific reference
range, 8.5 to 19); total T3 280 ng/dL( non pregnancy
reference range 60-180 ng/dL).
She has no previous history of thyroid disease. She is
feeling well apart from nausea and emesis intermittently
throughout the day for the past 2 weeks.
On examination her thyroid is normal in size without
nodules or tenderness. She has no opthalmopathy.
16. Question
Which of the following is the next best step?
A- Start MMI.
B- Start PTU.
C- Obtain a radioactive iodine uptake and scan.
D- Repeat the thyroid function tests in 2 weeks.
E-Thyroid ultrasound.
17. Comments
• This patient most likely has gestational thyrotoxicosis
due hCG stimulation of the thyroidal TSH receptor.
• The presence of nausea and vomiting and the absence of
stigmata of Graves’ disease support this diagnosis.
However Graves hyperthyroidism can also present in
the first trimester.
• RAI scanning is contraindicated in pregnancy and
thyroid ultrasound will not help to distinguish between
gestational thyrotoxicosis and Gaves’ disease.
• Obtaining a TRAb and /or TPO Ab level might be
helpful in determining the etiology of the thyrotoxicosis.
But this option is not provided.
18. Comment 2
• ATDs are not indicated for the treatment of gestational
thyrotoxicosis.
• In this patient in whom the etiology of hyperthyroidism
is not currently clear, and who does not have highly
elevated thyroid hormone level, it is reasonable to
provide supportive care and to repeat thyroid function
test 2 weeks.
• Serum hCG levels peak at 8-10 weeks gestation, so if this
gestational thyrotoxicosis , it is anticipated that thyroid
function will start to improve by 12 weeks’ gestation.
• Worsened hyperthyroidism when thyroid function is
repeated in 2 weeks would strongly suggest the presence
of Graves’ disease.
21. Changes in HCG level During Gestation
Maternal concentrations of serum TSH and hCG as a function of gestational age.
The decrease in serum TSH at approximately 10 week’s gestation may be due to
thyrotropic effects of hCG.
Glinoer D, et al. Regulation of maternal thyroid during pregnancy. J Clin Endocrinol Metab 1990;
71:276.
