Undiagnosed, untreated thyroid disease in pregnant women has a significant risk of adverse outcomes for both the mother and baby. Screening to identify pregnant women who are hypothyroid or hyperthyroid has been advocated using 2 approaches; the first is universal screening of all pregnant women and the second is a case-finding approach (which involves screening only pregnant women with symptoms of thyroid disease). Both these approaches are controversial. Recent published guidelines recommended using case-finding approach for pregnant women identified as high risk for thyroid disease. However, a report published soon after the guidelines demonstrated that screening of only high-risk pregnancies failed to detect 30% of women with hypothyroid and nearly 70% of hyperthyroid women. Currently, no medical organization recommends universal screening for thyroid disease.
This randomized study investigated the effectiveness of thyroid disease treatment during pregnancy on the incidence of maternal and neonatal adverse outcomes and compared the ability of universal screening and case-finding to detect thyroid dysfunction. A total of 4562 women in their first trimester of pregnancy were randomized to either case-finding approach (n = 2282) or universal screening (n = 2280). Women in the 2 groups were classified as high risk or low risk based on the presence of risk factors for thyroid disease. Women with hypothyroidism were defined as having thyroid stimulating hormone (TSH) greater than 2.5 mIU/L and being positive for thyroid peroxidase antibody, and women with hyperthyroidism were defined as having undetectable TSH concentration and elevated free T4. The sera of all women in the universal screening group and women at high-risk in the case-finding group were immediately tested for TSH, free T4, and thyroid peroxidase antibody. Women with hypothyroidism were treated with levothyroxine; women with hyperthyroid were managed with anti-thyroid medication.
There were no significant differences in adverse outcomes between the universal and case-finding screening groups. Fewer low-risk women in the universal screening group had adverse outcomes compared with low-risk women in the case-finding group.
The majority of women with thyroid disease were missed by the case-finding approach.
These findings show that screening pregnant women for thyroid disease using the case-finding approach is not associated with a greater decease in adverse outcomes than universal screening. Adverse outcomes appear to be less likely among low-risk women in the universal screening group than among low-risk women in the case-finding group.