The Strength of the Thyroid Immune Response and Miscarriages

The presence of thyroid autoantibodies in the first trimester of pregnancy is associated with an increased rate of miscarriage. Women who are positive for thyroglobulin (Tg) or thyroid peroxidase (TPO) autoantibodies, have been found to have a miscarriage rate of ~17% compared with ~8% in antibody negative women. In this study, we assessed the titer levels of thyroid autoantibodies in women with hypothyroidism and a history of miscarriage.

Methods:

We conducted a retrospective case study using the Mount Sinai Data Warehouse over the ten years from January 1st, 2011, to October 12th, 2021. Women between the ages of 18 and 40 who had a diagnosis of hypothyroidism, were taking T4 therapy, and who had been reviewed because of pregnancy were included. Also, if measured, the titer levels of TPO and Tg antibodies were also recorded. The primary outcome was a miscarriage, and the secondary outcome included the antibody titer levels.

Results:

We identified 2,398 women who were both pregnant and diagnosed with hypothyroidism. 173 (7.2%) women were found to have had a miscarriage. Of those 173 women, 37 (21.4%) had multiple, defined by at least two, miscarriages. It was noted that 81 (46.8%) women had thyroid autoantibodies (anti-Tg, anti-TPO, or both) tested and 46 (56.8%) of them were antibody positivity compared to 9-15% positivity in the normal female population of similar age. We also found that 43 (93.5%) of the 46 women with a miscarriage had levels two times the upper limit of “normal” autoantibodies for either Tg, TPO, or both.

Discussion/Conclusion:

This study demonstrated that women with high thyroid autoantibody titers are at a high risk of miscarriage. Our data also showed that less than 50% of women with hypothyroidism who suffered a miscarriage had thyroid autoantibodies checked by their physicians. When they were tested, the majority (93.5%) were not only positive but their levels were elevated to more than twice the upper limit considered “normal” in the assays employed. Given the risk of the health complications caused by miscarriages, improved awareness of this issue is key. Health care providers should check thyroid autoantibodies at least once in order to identify an at-risk pregnancy.