Hyperthyroidism and Fertility

This morning I attended a terrific lecture by Drs Murji and Sobel (Mount Sinai) on the subject of hyperthyroidism and pregnancy.

When women of reproductive age are hyperthyroid, it can be difficult to become, and stay, pregnant.

How do you know if you are hyperthyroid?

Hyperthyroid symptoms include elevated heart rate; more symptoms may be found here.  However, the signs can be subtle, so nearly all fertility programmes now screen all new patients for thyroid disorders at the first visit, regardless of symptoms.

If hyperthyroidism is suspected from the initial blood test, we will often order a complete screen, including:

• Blood tests:

(repeat) TSH: the initial screening test

T4: the thyroid hormone

T3: a second thyroid hormone, of value before treatments start

TRAb: Thyroid receptor antibodies

• Thyroid ultrasound
• Physical exam

The most common reason for hyperthyroidism in reproductive aged women is elevated levels of thyroid receptor antibodies.  The condition is known as Graves disease.

Maternal significance of Graves Disease

A  Reproductive Endocrinologist is generally not the best person to manage Graves disease.  Your RE (or, if pregnant, your Ob/Gyn) will refer you to an Endocrinologist with experience in treating thyroid disorders.

If Graves is identified up before pregnancy, one common treatment option is radioactive iodine.  Iodine is picked up by the thyroid, so radioactive iodine will preferentially affect the thyroid…effectively ablating (shrinking) it.

But radioactive iodine is not appropriate after 10 weeks of pregnancy.  While it will ablate mum’s thyroid, it would also ablate baby’s.

Instead, a medication called PTU is standard of care while pregnant.  PTU does cross the placenta…which is actually a good thing, for it can act to protect the baby as well as the mother.  PTU seems to be safe and effective, with generally minor side effects (although very occasional agranulocytosis (WBC <0.5)).

Alternatives to PTU include iodine therapy, Celestone (betamethasone), and thyroidectomy.  (Another medication, methimazole, is in the same class of medication as PTU but may not be as safe during pregnancy).

If she isn’t feeling well, propanolol stabilizes mum (heart rate, BP, etc) but doesn’t treat the underlying disease.

Miscarriage, preterm delivery rates, and pre eclampsia are higher in uncontrolled Graves disease, but in general, outcomes are very good with controlled Graves.  As long as we have good control of the thyroid before pregnancy, we do not usually see difficulties for mum or baby.

(A thyroid storm is a rare clinical diagnosis of a lifethreatening hypermetabolic state with over 50% mortality.  It only happens in women with out of control thyroid plus an added stressor such as pneumonia or ovarian hyperstimlation).

Will the baby be affected?  Less than 5% of the time…because when we treat the mum, we are treating the baby.  When babies are affected, we will usually note a goitre (enlarged thyroid) seen at the routine 18wk u/s scan.

For an in depth review, consider this paper from Nature Reviews (formerly Nature Clinical Practice).

For hypothyroidism (low thyroid), I’ll be writing a new post.

TGH

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