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February 17, 2022
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Overt thyroid disease prevalence supports universal thyroid screening during pregnancy

Recommendations on whether all pregnant women should undergo universal thyroid screening vary around the globe.

Several European societies, including the Italian Thyroid Association, Spanish Thyroid Association and European Thyroid Association, support universal thyroid screening for pregnant women. In the U.S., however, the American Thyroid Association endorsed targeted screening based on a series of risk factors in its 2017 guideline for managing thyroid disease during pregnancy and postpartum.

Alex Stagnaro-Green, MD, MHPE
Stagnaro-Green is regional dean at the University of Illinois College of Medicine in Rockford.

Much of the universal thyroid screening debate focuses on whether subclinical hypothyroidism poses risk for pregnant women and should be treated. Multiple studies have found overt hypothyroidism and overt hyperthyroidism increase risks for complications during pregnancy, such as spontaneous abortion, preterm delivery, preeclampsia and gestational hypertension. With more than 1% of the U.S. population having either overt hypothyroidism or overt hyperthyroidism, prevalence is high enough to warrant universal thyroid screening in this country, according to Alex Stagnaro-Green, MD, MHPE, regional dean at the University of Illinois College of Medicine in Rockford.

Stagnaro-Green will discuss universal thyroid screening for pregnant women at the USC Jorge H. Mestman Endocrine and Pregnancy Symposium taking place virtually Feb. 19. Before the symposium, Healio spoke with Stagnaro-Green about current recommendations for thyroid screening during pregnancy, some of the evidence supporting universal screening and further research needed.

Healio: What practices have surrounded thyroid screening for pregnant women since the publication of the ATAs 2017 guidelines?

Stagnaro-Green: Targeted screening has been the main approach, screening people who are at risk. If you have type 1 diabetes, you’re at risk for thyroid disease, and that would be a group you’d recommend for screening, or if a family member has autoimmune disease. The American Thyroid Association 2017 guideline lists the 10 criteria for screening.

Overall, I do believe more patients are getting screened. There are data showing that the percentage of individuals who are pregnant and are getting screened is increasing. The problem is in interpreting that data, most of those studies are done in places that focus on thyroid pregnancy, so the data are somewhat biased.

Healio: Why do you support universal thyroid screening?

Stagnaro-Green: I looked at the 10 criteria that were developed by James Maxwell Glover Wilson and Gunnar Jungner in 1968, which serve as the pillars you need to meet for society to accept universal screening of a disorder, and how that relates to the thyroid hormonal problems that could present in pregnancy. I then reviewed the literature to see if each of these thyroid conditions meet the 10 criteria.

If you look at overt hypothyroidism, it meets all of the criteria. If you look at overt hyperthyroidism, it meets of all the criteria except for one — a cost-effectiveness analysis, which has never been done for overt hyperthyroidism. But in fact, there is really not much more of an added expense; if you are screening for overt hypothyroidism, you’re going to identify individuals who may have overt hyperthyroidism.

Everyone agrees that overt hypothyroidism and overt hyperthyroidism in pregnancy need to be treated. I conducted a study published in 2019 in Thyroid that took a look at the prevalence of overt hypothyroidism and overt hyperthyroidism as well as subclinical hypothyroidism. Overt hypothyroidism was found in 0.5% of the population. Overt hyperthyroidism prevalence is 0.65%. If you add that together, it’s 1.15%. A little more than one out of every 100 women are going to have overt thyroid disease, and everyone agrees that overt hypothyroidism and overt hyperthyroidism have a negative impact on the pregnancy and the mother. The argument I make is straight forward. Simply, identifying and treating overt thyroid disease in pregnancy has enough of a beneficial impact to warrant universal screening.

A separate but related issue is whether or not to screen for subclinical hypothyroidism in pregnancy. The 2017 ATA Guidelines on Thyroid and Pregnancy recommend treating women with subclinical hypothyroidism (thyroid-stimulating hormone 4-10 mIU/mL) who are pregnant if they are thyroid antibody positive, but it only states that levothyroxine may be considered for women with subclinical hypothyroidism who are thyroid antibody negative. Data published subsequent to the 2017 ATA guideline provides moderately strong evidence that treating subclinical hypothyroidism during pregnancy in thyroid antibody negative women decreases preterm delivery and increases IQ in the offspring. Accordingly, I believe that the ATA Guidelines on Thyroid and Pregnancy need to be updated to recommend that all women with subclinical hypothyroidism, irrespective of thyroid antibody status, be treated.

Healio: Why is universal thyroid screening so controversial? What research has been done on this topic?

Stagnaro-Green: It’s controversial because you’re recommending screening 3 million women in the United States. The main area of controversy, however, relates to the benefit of treating pregnant women with subclinical thyroid disease. That discussion has obfuscated the fact that screening and treating overt thyroid disease by itself meets all of the criteria for universal screening.

Have there been definitive studies showing universal screening is more effective? The answer is somewhat nuanced. There have been two trials published in The New England Journal of Medicine, and both of them treated subclinical hypothyroidism. They looked at the primary outcome of IQ in children at the ages of 3 and 5 years and found no difference. The problem with both of those studies is they started screening in the second trimester, and the belief is that you need to screen women very early in pregnancy — in the first trimester — if you’re going to decrease the miscarriage rate and improve IQ in the offspring. The definitive study that needs to be done is screening all women early in pregnancy — prior to 8 weeks’ gestation — and then randomly assigning half of those women to thyroid hormone intervention and half to a placebo control.

Healio: What are some of the risks of not performing universal thyroid screening?

Stagnaro-Green: The risk of not doing universal screening is most of the cases of overt thyroid disease will never be identified or treated. The other risk is, if you believe that subclinical hypothyroidism is an increased risk for miscarriage and preterm delivery, then by not identifying them and treating them, those individuals will be at greater risk.

Healio: Why do some societies support universal thyroid screening, and some dont?

Stagnaro-Green: There are two reasons. First, as discussed above, the field is focusing so much on the subclinical hypothyroidism controversy, it is ignoring the data on identifying and treating overt thyroid disease. Secondly, the optimal study for the impact of treating subclinical thyroid disease in pregnancy has not yet been done.

References:

For more information:

Alex Stagnaro-Green, MDMHPE, can be reached at asg@uic.edu.

He will speak on this topic as part of the USC Jorge H. Mestman Endocrine and Pregnancy Symposium taking place virtually Feb. 19.

Register at: keckusc.cloud-cme.com/course/courseoverview?P=5&EID=3712