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Recommendations for managing thyroid disease in pregnancy
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Thyroid disease is the second most common endocrine disorder among women of reproductive age, and endocrinologists managing women with thyroid disease must consider several important points when developing a treatment plan before, during and after pregnancy, according to Caroline Nguyen, MD, assistant professor of clinical medicine at Keck School of Medicine at USC.
Nguyen recently spoke with Endocrine Today about treating pregnant women with thyroid cancer, new guidelines for hypothyroidism in pregnancy and the importance of preconception counseling in Graves’ disease.
How should an endocrinologist manage a pregnant patient who has already been treated for thyroid cancer?
Nguyen: How your patient is doing before pregnancy is a very good indication of how they are going to do during pregnancy and in the postpartum period. This means that if you have a low-risk patient before pregnancy, they’re likely to do very well throughout pregnancy and afterward. If you have a patient who had known structural disease before pregnancy, these are the patients that we have to be more concerned about during pregnancy and the postpartum period, as they may experience progression of their structural disease.
Many will come to you with thyroid-stimulating hormone suppression. It is safe to continue the TSH suppression into pregnancy. If you are suppressing your patient for thyroid cancer, the recommendation is to go ahead and increase the thyroid dose to accommodate the increased needs in pregnancy to maintain the TSH at the same level.
Thyroid cancer is often detected during pregnancy. How should clinicians manage these patients?
Nguyen: Postponing treatment for cancer discovered during pregnancy has not been shown to alter outcomes. In fact, studies have not been able to show that delaying surgery for thyroid cancer detected during pregnancy until after delivery has led to any increased recurrence or change in mortality.
The American Thyroid Association guideline s for managing hypothyroidism in pregnancy recently changed. What should clinicians know?
Nguyen: The 2017 ATA guideline for managing thyroid disease in pregnancy reflects a change in the TSH upper limit range. Where it used to be between 2.5 mIU/L and 3 mIU/L, the guideline authors found that to be too aggressive and it was leading to overtreatment of patients. The current guideline recommends that we use trimester-specific, lab-specific reference ranges for the treatment of pregnant women with thyroid disease. Many times, it can be difficult for practitioners to get access to these specific reference ranges. The ATA recommends that you use the non-pregnancy TSH reference range and subtract 0.5 mIU/L. This tends to work for most patient populations.
Using those new guidelines, we found that, when TSH is between 2.5 mIU/L and 10 mIU/L in a pregnant patient, the recommendation is to check the thyroid peroxidase (TPO) antibody levels. The TPO antibody level helps to risk-stratify patients to see whether treatment would be beneficial.
There are clear areas regarding whether or not to treat: We treat patients who are TPO antibody positive with a TSH between 4 mIU/L and 10 mIU/L. We typically do not treat women who are TPO antibody negative with a TSH between 2.5 mIU/L and 4 mIU/L.
Some areas are considered “gray zones,” where the recommendations state the physician can consider treatment. These are patients with TPO antibody positivity and a TSH level between 2.4 mIU/L and 4 mIU/L, and TPO negative women with a TSH level between 4 mIU/L and 10 mIU/L. It will be exciting to see what comes in the future with trials involving women who fall into these two categories.
What are the recommendations regarding antithyroid drug use during pregnancy ?
Nguyen: More data suggests that propylthiouracil (PTU) is associated with fetal malformations. There are different types of malformations, so the recommendation is still to use PTU during the first trimester of pregnancy. However, our goal should be to avoid antithyroid drug use in the early part of pregnancy. We know the period of teratogenicity is between weeks 6 through 10, and often many patients don’t come to our office until this time. I have to emphasize that preconception counseling for our patients is so important. It means discussing pregnancy planning, the use of antithyroid drugs and possibly the use of definitive therapy.
With that in mind, how should clinicians treat pregnant women with Graves ’ hyperthyroidism?
If a woman comes to you and asks if they should continue with their antithyroid medication, undergo radioactive iodine therapy or a total thyroidectomy, my recommendation is to look at the patient and see how well controlled they are and obtain a TSH receptor antibodies (TRAb) level. If this level is very high — meaning, greater than three times the upper limit of normal — we know this is associated with greater risk for fetal hyperthyroidism. This may alter the treatment plan you recommend for your patient. After radioactive iodine, the TRAb level is going to rise in the 6 months posttreatment and it can stay quite elevated before it gradually comes down, which can take years. With antithyroid drugs or total thyroidectomy, we know the TRAb levels come down right away with treatment. These are some considerations to think about when meeting with Graves’ hyperthyroid patients. All women with Graves’ disease who are sexually active should be using contraception. Graves’ disease in itself does pose risks to the fetus. – by Regina Schaffer
Disclosure: Nguyen reports no relevant financial disclosures.