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TPOAb positivity predicts duration of thyroid dysfunction in pregnancy
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Among women positive for thyroid peroxidase antibodies, subclinical hypothyroidism and hypothyroxinemia diagnosed in the first trimester are likely to resolve later in pregnancy; however, subclinical hyperthyroidism is likely to persist, according to findings published in Thyroid.
“Additional knowledge on the natural course of gestational thyroid dysfunction is crucial for improving the clinical interpretation of thyroid function tests during pregnancy,” Jianxia Fan, MD, PhD, of the International Peace Maternity and Child Health Hospital and the school of medicine at Shanghai Jiao Tong University in Shanghai, and colleagues wrote. “Identification of women with persistent disease and quantification of its risk factors can improve future studies on the consequences of persistent and transient dysfunction, as well as the relevance of third trimester thyroid (dys)function and the risk of adverse pregnancy and child outcomes.”
Fan and colleagues measured thyroid-stimulating hormone, thyroxine, triiodothyronine and thyroid peroxidase antibodies (TPOAb) in 42,492 women (median age, 30 years) who provided a first trimester blood sample from 2013 and 2016 at the International Peace Maternity and Child Health Hospital in Shanghai. TPOAb positivity was confirmed by a TPOAb measure of at least 6 IU/mL, according to the researchers, who noted that thyroid treatment was not delivered to the included participants.
Participants who had a TSH level above the 97.5th percentile and T4 between the 2.5th and 97.5th percentile were considered to have subclinical hypothyroidism, which remained in the third trimester in 24.8% of the women diagnosed with the condition during the first trimester. The researchers wrote that it was less likely that the condition would remain in women with TPOAb positivity vs. those without (OR = 0.33; 95% CI, 0.25-0.43). They also noted that “TSH below roughly 5 mU/L at the time of diagnosis was associated with an up to 50% lower risk of persistency.”
When participants had a T4 level below the 2.5th percentile and a TSH level between the 2.5th and 97.5th percentile, they were diagnosed with hypothyroxinemia by the researchers, who noted that this condition held for 17.7% of the women from the first to third trimesters. The researchers also found that TPOAb positivity reduced the chances of sustained hypothyroxinemia (OR = 0.48; 95% CI, 0.25-0.91).
TSH levels below the 2.5th percentile in combination with a T4 level between the 2.5th and 97.5th percentile constituted subclinical hyperthyroidism, and this held into the third trimester for 20.9% of those who presented with the condition in the first trimester. This was more likely to occur for women with thyroid antibody positivity vs. those without (OR = 1.86; 95% CI, 1.57-5.89). In addition, a TSH below the 2.5th percentile and a T4 above the 97.5th percentile confirmed overt hyperthyroidism and the researchers noted that “a higher [T4] was associated with an up to twofold higher risk of persistency” of the condition into the third trimester.
“This suggests that the majority of gestational thyroid dysfunction entities diagnosed during early pregnancy represent a transient form of thyroid dysfunction. Most likely, the transient nature of thyroid dysfunction during early pregnancy is caused by the increased demand for thyroid hormone during early pregnancy,” the researchers wrote. “These data provide new insights into thyroid physiology during pregnancy and may aid clinicians in their clinical risk assessment of women with gestational thyroid dysfunction.” – by Phil Neuffer
Disclosures: The authors report no relevant financial disclosures.
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