Thyroid Disease in Pregnancy Fact Sheet Joseph Breuner MD 5/09/05
3 take-home points: 1.(almost) never check thyroid tests in hyperemesis
2. Treat thyroid disease in pregnancy to a high normal T4 concentration
3. Hypothyroid women who become pregnant will need a dose increase, begin with 25-50%.
Thyroid fxn during normal pregnancy: TBG goes up, this increases total T4 and T3 but not free T4.
HCG has weak thyroid stimulating activity.
HCG-mediated hyperthyroidism: 3 syndromes are described
A. 10-20% of normal pregnancies have subclinical hyperthyroidism during peak HCG activity. No treatment.
B. 60% of women with hyperemesis have subclinical or mild overt hyperthyroidism, which resolves without
C. 60% of women with trophoblastic disease (mole or choriocarcinoma) have hyperthyroidism.
Hyperthyroidism complicating pregnancy: causes spontaneous abortion, premature labor, low birth weight,
stillbirth, preeclampsia, congestive heart failure.
Graves hyperthyroidism is most common cause, complicating 1/500 (0.2%) of pregnancies.
Diagnosis of hyperthyroidism in pregnancy: TSH< 0.1 and a high serum free T4.
Treatment of hyperthyroidism in pregnancy: goal is to maintain mother’s serum free T4 concentration in
the high normal range using the lowest drug dose. Check free T4 q 4 weeks.
Drugs of choice are propylthiouracil or methimazole, PTU is preferred because of rare fetal defects with
Beta-blockers can be used for symptom control.
Fetal Graves: measure TSH receptor stimulating antibodies in Moms with Graves in 3rd trimester, values 5-
fold higher than normal are associated with neonatal hyperthyroidism. Symptoms of fetal hyperthyroidism
include fetal tachycardia (>160), fetal goiter, advanced bone age, poor growth, and craniosynostosis are
manifestations of fetal hyperthyroidism.
Nursing on PTU or methimazole is safe.
Hypothyroidism in pregnancy: rare because low T4 causes anovulation and 1st trimester SAB. Effects on
surviving fetuses for untreated hypothyroidism are severe: low birth wt, congenital anomalies, perinatal
mortality, and developmental delay.
Treatment of hypothyroidism in pregnancy: goal is to normalize the maternal TSH. 75% of women with
pre-existing hypothyroidism will need a higher dose in pregnancy. Measure TSH 4-8 weeks after conception,
4-6 weeks after any dosage change, and at least once a trimester.
Goiter: mean increase in volume with pregnancy is 18%, clinically detectable in some women.
Nodules: radionuclide scanning is contraindicated in pregnancy, so pregnant women with a dominant mass
need fine-needle aspiration.
Postpartum syndromes: 5-10% of women have one of the following three syndromes
1. transient hyperthyroidism followed by recovery—treat only if symptomatic with a beta-blocker.
2. Transient hyperthyroidism, followed by transient or rarely permanent hypothyroidism. Treat with
synthyroid x six months then taper to see if thyroid fxn returns.
3. Transient or permanent hypothyroidism, treat as in #2.
Question and answer: from ACOG practice bulletin number 37, august 2002: thyroid disease in pregnancy
What laboratory tests are used to diagnose and manage thyroid disease during pregnancy?
TSH every 4 to 6 weeks
Free T4, as this is unaltered by thyroid binding globulin changes in pregnancy
Free T3 only pursued in patients with thyrotoxicosis with suppressed TSH but normal FT4.
Thyroid Stimulating Hormone receptor antibodies, can be either stimulatory (TSI) or inhibitory (TBII) and
antimicrosomal antibodies. Extremely high maternal TSI levels can cause neonatal graves; though practically
endocrinologists measure this and perinatologists do not.
What medications can be used to treat hyperthyroidism and hypothyroidism in pregnancy, and how should they
be administered and adjusted during pregnancy?
Hyperthyroidism in pregnancy is treated with thiamides, specifically PTU and methimazole, which decrease
thyroid hormone synthesis by blocking iodide organification. Both medicines are safe in pregnancy and
breastfeeding. They both can suppress fetal and neonatal thyroid function, but this is usually transient and
rarely requires therapy.
Treatment goal of hyperthyroidism in pregnancy is to maintain the FT4 in the high normal range using the
lowest possible dose of thioamides.
One side effect of thioamides is agranulocytosis, incidence is 0.1-0.4%. it usually presents with fever and sore
throat. Instruct your patient to call if they get these symptoms and draw a CBC.
Beta-blockers may be used during pregnancy to ameliorate the symptoms of thyrotoxicosis until thioamides
decrease hormone levels.
Iodine 131 is contraindicated in pregnant women because of the risk of fetal thyroid ablation, so women
should avoid pregnancy for 4 months after I-131 treatment.
Treatment of hypothyroidism in pregnant women is the same as for nonpregnant women; administer
levothyroxine at sufficient doses to normalize TSH levels. Adjust at 4 week intervals. Thyroid requirements
increase 25-50% with pregnancy.
What changes in thyroid function occur with hyperemesis gravidarum, and should TFT’s be performed
routinely in women with hyperemesis?
Hyperemesis gravidarum is associated with biochemical hyperthyroidism but rarely with clinical
hyperthyroidism and is largely transitory, requiring no treatment. Routine measurements of thyroid function are
not recommended in patients with hyperemesis gravidarum unless other overt signs of hyperthyroidism are
How is thyroid storm diagnosed and treated in pregnancy?
Thyroid storm occurs in 1% of pregnant patients with hyperthyroidism, and carries a high risk of maternal
Signs and symptoms are fever; tachycardia out of proportion to the fever; changed mental status, including
restlessness, nervousness, confusion and seizures; vomiting; diarrhea; and cardiac arrhythmia.
Often there is an inciting event—infection, surgery, labor or delivery.
Severe consequences if untreated are shock, stupor and coma.
Obtain serum FT4, FT3 and TSH but don’t withhold treatment pending results
Use these medications: 1. PTU 600-800 mg orally, stat, then 150-200 mg orally q 4-6 hrs. 2. 1-2 hrs after PTU
administration, give saturated solution of potassium iodide, 2-5 drops orally every 8 hrs. (or sodium iodide .
5-1.0 gms IV q 8 hrs, or lugol’s solution, 8 drops every 6 hrs, or lithium carbonate 300 mg po q 6 hrs). 3.
Dexamethasone, 2 mg IV or IM q 6 hrs x 4 doses. 4. Propranolol, 1-2 mg IV every 5 minutes for a total of 6
mg, then 1-10 mg IV q 4 hrs. 5. Phenobarbital, 30-60 mg orally every 6-8 hrs as needed for extreme
How should a thyroid nodule or thyroid cancer during pregnancy be assessed?
Incidence of thyroid cancer in pregnancy is 1 per 1,000.
Any thyroid nodule discovered during pregnancy should be diagnostically evaluated, because malignancy will be
found in up to 40% of these nodules.
Pregnancy itself does not appear to alter the course of thyroid cancer.
Ultrasound and fine needle aspiration should be performed on palpable nodules.
If cancer is diagnosed, a multidisciplinary treatment plan should be determined. Options include pregnancy
termination, treatment during pregnancy, and preterm or term delivery with treatment after pregnancy.
Decision will be affected by gestational age at diagnosis and tumor characteristics.
How is postpartum thyroiditis diagnosed and treated?
Occurs in 5%of women who have no history of thyroid disease.
44% have hypothyroidism, while the remainder are evenly split between thyrotoxicosis and thyrotoxicosis
followed by hypothyroidism.
Diagnosis is made by documenting new-onset abnormal levels of TSH or FT4 or both. If dx is in doubt,
measuring antimicrosomal or thyroperoxidase antithyroid peroxidase antibodies may be useful to confirm the
Need for treatment is unclear: None of the women with thyrotoxicosis require treatment. 40% of the women
with hypothyroidism require treatment, and 11% will have permanent hypothyroidism.
Because treatment is rarely beneficial, asymptomatic women needn’t be screened. Test women who develop a
goiter in pregnancy or postpartum or those who develop thyroid symptoms: excess fatigue, weight gain, dry
skin, dry hair, cold intolerance, persistent amenorrhea, difficulty concentrating, depression, nervousness or
Which pregnant patients should be screened for thyroid dysfunction?
Perform indicated testing of thyroid function in women with a personal history of thyroid disease or symptoms
of thyroid disease.
The performance of TFT in asymptomatic pregnant women who have a mildly enlarged thyroid is not
Development of a significant goiter or distinct nodules should be evaluated as in any patient.
An observational study of tsh levels drawn for maternal serum AFP screening compared IQ levels by group of
children when they were 8 years old. Children of hypothyroid women and controls had no difference in IQ
level. IQ scores differed significantly between children of untreated hypothyroid women and contols but not
between children of untreated and treated hypothyroid women. Among the children of untreated women, 19%
had full-scale IQ scores of 85 or lower, compared with only 5% of the children of women with normal thyroid
Summary of recommendations:
Level A-good and consistent scientific evidence
Levels of TSH or FT4 should be monitored to manage thyroid disease in pregnancy.
Level B-limited or inconsistent scientific evidence
Either PTU or methimazole can be used to treat pregnant women with hyperthyroidism.
Thyroid function tests are not indicated in asymptomatic pregnant women with slightly enlarged thyroid glands.
Level C –consensus and expert opinion
There is no need to measure TFT’s routinely in women with hyperemesis
There are insufficient data to warrant routine screening of asymptomatic pregnant women for hypothyroidism.
Indicated testing of thyroid function may be performed in women with a personal history of thyroid disease or
symptoms of thyroid disease
The presence of maternal thyroid disease is important information for the pediatrician to have at the time of
Thyroid nodules should be investigated to rule out malignancy
1. 24 y/o G1P0 at10 weeks is admitted to the hospital with hyperemesis gravidarum. You are the service
chief. The patient has lost 5% of her weight and has a 30 point drop in systolic BP and a 15 point pulse
rise in the emergency room. After rehydration, her posturals have a 15 point systolic drop and her pulse is
90 and does not increase with standing. Your intern would like to check some thyroid tests.
2. What do you think?
3. If you check them, what would you expect to see in terms of TSH, total T4 and free T4?
4. Which patients would merit treatment with PTU?
5. Your 32 y/o patient is trying to get pregnant and has taken 0.05 mg of synthroid for the last 5 years. Her
TSH is stable at 2.5. On her 3rd cycle, she gets pregnant and wonders whether her thyroid dose needs any
special attention .
6. How soon should it be checked?
7. Should her dose be changed?
9. By how much?
10. What risks ensue from undertreating her thyroid—i.e., leaving her mildly hypothyroid?
11. The same patient in question 1 presents at 16 weeks with more vomiting and complains of eye discomfort.
What condition are you thinking about?
12. What clinical signs would support the diagnosis?
13. What lab tests would make a diagnosis of hyperthyroidism?
14. Where should you maintain the free T4?