2. Thyrotoxicosis in pregnancy:
| a. | is usually due to a solitary adenoma | False |
| b. | usually occurs as new disease as a result of HCG stimulation of the thyroid | False |
| c. | occurs once in every five hundred pregnancies | True |
| d. | may be treated with radioactive iodine as the drug does not cross the placenta | False |
| e. | carries little extra risk to the baby | False |
| f. | the baby is at risk of neonatal hyperthyroidism | True |
| g. | the baby is at risk of neonatal hypothyroidism | True |
| h. | beta-blocking drugs are contra-indicated | False |
| i. | the major maternal risk is congestive cardiac failure | True |
See also MCQ 5, question 33 and MCQ10, question 13.
Thyrotoxicosis occurs in about one pregnancy in every 500.
It is almost always due to pre-existing Graves' disease.
All such patients should be stabilised before pregnancy.
Some of the signs & symptoms of hyperthyroidism occur commonly in normal pregnancy:
palpitations,
tiredness,
thyroid enlargement etc.
So the diagnosis may easily be missed.
Features particularly pointing to thyrotoxicosis, not being particularly associated with pregnancy alone are:
weight loss,
tremor,
tachycardia,
lid lag,
exophthalmos.
There is an association with hyperemesis gravidarum.
Patients with excessive vomiting in early pregnancy should have their thyroid function checked.
It is believed to be due to thyroid stimulation from the higher than normal levels of HCG which are found with hyperemesis.
Not surprisingly, hydatidiform mole is particularly associated with thyroid overactivity.
Carbimazole and thiouracil are the drugs commonly used.
Carbimazole may cause agranulocytosis, but this is rare.
The BNF includes the following advice:
"Counselling. Warn patients to tell doctor immediately if:
sore throat,
mouth ulcers,
bruising,
fever,
malaise,
or non-specific illness occur".
There is a small risk of severe liver disease with thiouracil.
The FDA put out a warning in 2009.
The key advice in relation to pregnancy was:
"Rare cases of embryopathy, including aplasia cutis, have been reported with use of methimazole (carbimazole) during pregnancy.
No such cases have been reported with propylthiouracil use during pregnancy.
Therefore, propylthiouracil may be more appropriate for patients with Graves’ disease who are in their first trimester of pregnancy".
It also advised close monitoring for signs of liver problems, especially in the first 6 months of treatment.
Both drugs can be given during lactation.
Thiouracil is present in smaller amounts in milk that carbimazole.
So, it is preferred, all else being equal.
Beta-blockers may be used to ease symptoms while the condition is being brought under control.
Radioactive iodine will cross to the baby, so is contraindicated.
Surgery may be necessary in rare cases not responding to drug therapy, .
If control is poor, there is an increased risk of:
fetal abnormality,
miscarriage,
fetal death in utero,
IUGR,
neonatal death.
With good control the risks mirror those of normal pregnancy.
Anti-thyroid drugs cross the placenta and may cause neonatal hypothyroidism and compensatory goitre.
Maternal thyroid autoantibodies may also cross the placenta.
They are thyroid stimulating, so may cause neonatal thyrotoxicosis, which has significant hazard for the baby.
Maternal risk is small, the main hazard being cardiac failure.
This is attributed to the adverse effect of the condition on the cardiac muscle at a time when the circulating volume has expanded greatly.