Treatment for Subclinical Hypothyroidism in Pregnancy
Whereas current guidelines recommend TPO antibody status in determining when to consider treatment for subclinical hypothyroidism, the new proposed guideline will instead recommend treatment based on the timing of the diagnosis of the subclinical hypothyroidism, with consideration of treatment during the first trimester, but not in the second or third trimester, based on newer evidence of the absolute risk for pregnancy complications and randomized trial data.
“The recommendations are now to no longer based on TPO antibody status, but instead according to the timing of the diagnosis of subclinical hypothyroidism,” Korevaar said.
Based on the collective data, “due to the low risk, we do not recommend for routine levothyroxine treatment in the second or third trimester groups with TSH levels under 10 mU/L now.”
“However, for subclinical hypothyroidism diagnosed in the first trimester, the recommendation would be that you can consider levothyroxine treatment,” he said.
While a clear indication for treatment in any trimester is the presence of overt hypothyroidism, or TSH levels over 10 mU/L, Korevaar underscored the importance of considering nuances of the recommendations that may warrant flexibility, for instance among patients with borderline TSH levels.
Spontaneous Normalization of Thyroid Levels in Pregnancy
Another new recommendation addresses the issue of spontaneous normalization of abnormal thyroid function during pregnancy, with several large studies showing a large proportion of subclinical hypothyroidism cases spontaneously revert to euthyroidism by the third trimester — despite no treatment having been provided.
Under the important proposed recommendation, retesting of subclinical hypothyroidism is suggested within 3 weeks.
“The data shows that a large proportion of patients spontaneously revert to euthyroidism,” Korevaar said.
“Upon identifying subclinical hypothyroidism in the first trimester, there will be essentially two options that clinicians can discuss with their patient — one would be to consider confirmatory tests in 3 weeks or to discuss the starting the lower dose levothyroxine in the first trimester,” he said.
In terms of overt hypothyroidism, likewise, if patients have a TSH levels below 6 mU/L in pregnancy, “you can either consider doing confirmatory testing within 3 weeks, or discussing with the patient starting levothyroxine treatment,” Korevaar added.
Overt Hyperthyroidism
For overt hyperthyroidism, no significant changes from current guidelines are being proposed, with the key exception of a heightened emphasis on the need for shared decision-making with patients, Korevaar said.
“We want to emphasize shared decision-making especially for women who have Graves’ disease prior to pregnancy, because the antithyroid treatment modalities, primarily methimazole (MMI) and propylthiouracil (PTU), have different advantages and disadvantages for an upcoming pregnancy,” he said.
“If you help a patient become involved in the decision-making process, that can also be very helpful in managing the disease and following-up on the pregnancy.”
Under the recommendations, PTU remains the preferred drug in overt hyperthyroidism, due to a more favorable profile in terms of potential birth defects vs MMI, with research showing a higher absolute risk of 3% vs 5%.
The guidelines further suggest the option of stopping the antithyroid medications upon a positive pregnancy test, with the exception of high-risk patients.
Korevaar noted that, if the treatment is stopped early in pregnancy, relapse is not likely to occur until after approximately 3 months, or 12 weeks, at which time, the high-risk teratogenic period, which is between week 5 and week 15, will have passed.
Current guidelines regarding whether to stop treatment in higher-risk hyperthyroid patients are recommended to remain unchanged.