February 17, 2022
4 minute read
Recommendations on whether all pregnant women should have universal thyroid screening vary around the world.
Several European societies, including the Italian Thyroid Association, the Spanish Thyroid Association, and the European Thyroid Association, support universal thyroid screening for pregnant women. In the United States, however, the American Thyroid Association endorsed targeted screening based on a series of risk factors in its 2017 guidelines for the management of thyroid disease in pregnancy and postpartum.
Much of the debate over universal thyroid screening revolves around whether subclinical hypothyroidism poses a risk to pregnant women and should be treated. Several studies have shown that manifest hypothyroidism and manifest hyperthyroidism increase the risk of complications during pregnancy, such as spontaneous abortion, premature delivery, preeclampsia, and gestational hypertension. With more than 1% of the US population suffering from overt hypothyroidism or overt hyperthyroidism, the prevalence is high enough to warrant universal thyroid screening in this country, according to Alex Stagnaro-Green, MD, MHPEregional dean of the College of Medicine at the University of Illinois at Rockford.
Stagnaro-Green will discuss universal thyroid screening for pregnant women at the USC Jorge H. Mestman Endocrinology and Pregnancy Symposium taking place virtually on February 19. Prior to the symposium, Healio spoke with Stagnaro-Green about current recommendations for thyroid screening in pregnancy, some of the evidence supporting universal screening, and further research needed.
Helio: What practices surrounded thyroid screening in pregnant women since the publication of the ATA‘2017 Guidelines?
Stagnaro-Green: Targeted screening has been the primary approach, screening those at risk. If you have type 1 diabetes, you are at risk for thyroid disease, and this would be a group you would recommend for screening, or if a family member has an autoimmune disease. The American Thyroid Association’s 2017 guideline lists the 10 screening criteria.
Overall, I believe more patients are getting tested. There is data showing that the percentage of people who are pregnant and getting tested is increasing. The problem is in the interpretation of this data, most of these studies are done in places that focus on thyroid pregnancy, so the data is somewhat skewed.
Helio: 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 that you must meet for society to accept universal screening for a disorder, and how that relates to the issues thyroid hormones that may be present during pregnancy. I then reviewed the literature to see if each of these thyroid conditions met all 10 criteria.
If you look at overt hypothyroidism, it meets all the criteria. If you look at overt hyperthyroidism, it meets all the criteria except one – a cost-effectiveness analysis, which has never been done for overt hyperthyroidism. But in fact, there really isn’t much more extra expense; If you screen for overt hypothyroidism, you will identify people who may have overt hyperthyroidism.
Everyone agrees that overt hypothyroidism and overt hyperthyroidism in pregnancy should be treated. I conducted a study published in 2019 in Thyroid which examined the prevalence of overt hypothyroidism and overt hyperthyroidism as well as subclinical hypothyroidism. Obvious hypothyroidism was found in 0.5% of the population. The prevalence of overt hyperthyroidism is 0.65%. If you add that up, it’s 1.15%. Slightly more than one in 100 women will have overt thyroid disease, and everyone agrees that overt hypothyroidism and overt hyperthyroidism have a negative impact on the pregnancy and the mother. My argument is simple. Simply, the identification and treatment of overt thyroid disease during pregnancy has enough 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 Thyroid and Pregnancy Guidelines recommend treating pregnant women with subclinical hypothyroidism (thyroid-stimulating hormone 4-10 mIU/mL) who are pregnant if they test positive for thyroid antibodies, but they only indicate that levothyroxine can be considered for women with subclinical hypothyroidism who are negative for thyroid antibodies. Data published following the 2017 ATA guideline provide moderately strong evidence that treatment of subclinical hypothyroidism during pregnancy in thyroid antibody negative women decreases preterm birth and increases offspring IQ. Accordingly, I believe the ATA’s Thyroid and Pregnancy Guidelines should be updated to recommend that all women with subclinical hypothyroidism, regardless of thyroid antibody status, be treated.
Helio: Why is universal thyroid screening so controversial? What research has been ended on this topic?
Stagnaro-Green: It’s controversial because you recommend testing 3 million women in the United States. The main area of controversy, however, concerns the benefits of treating pregnant women with subclinical thyroid disease. This discussion has obscured the fact that screening and treatment of overt thyroid disease alone meets all the criteria for universal screening.
Have there been definitive studies showing that universal screening is more effective? The answer is somewhat nuanced. Two trials have been published in Jhe New England Journal of Medicine, and both treated subclinical hypothyroidism. They looked at the primary IQ score in children aged 3 and 5 and found no difference. The problem with these two studies is that 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 want to reduce the miscarriage rate and improve the IQ in offspring. The definitive study that needs to be done is to screen all women early in pregnancy – before 8 weeks gestation – and then randomly assign half of these women to thyroid hormone intervention and the other half to a placebo control.
Helio: What are some risks of do not carry out universal thyroid screening?
Stagnaro-Green: The risk of not doing universal screening is that most cases of overt thyroid disease will never be identified or treated. The other risk is that if you think subclinical hypothyroidism is an increased risk for miscarriage and preterm delivery, then by not identifying and treating them, these people will be at higher risk.
Helio: Why Some Companies Support Universal Thyroid screening, and some gifts‘you
Stagnaro-Green: There are two reasons. First, as noted above, the field focuses so much on the controversy of subclinical hypothyroidism that it ignores data on the identification and treatment of overt thyroid disease. Second, the optimal study on the impact of treatment of subclinical thyroid disease during pregnancy has yet to be performed.
For more information:
Alex Stagnaro GreenMDMHPEcan be contacted at [email protected]
He will speak on this topic at the USC Jorge H. Mestman Symposium on Endocrinology and Pregnancy to be held virtually on February 19.