Association between negative antithyroid peroxidase antibodies subclinical hypothyroidism and adverse perinatal outcomes diagnosed with different criteria in the third trimester of pregnancy

Abstract

Background: The effect of subclinical hypothyroidism (SCH) on adverse perinatal
outcomes is unclear, and thyroid-stimulating hormone (TSH) reference values in
pregnancy are controversial. Objective: To evaluate the effects of thyroid peroxidase
antibody (TPOAbs) negative SCH on perinatal outcomes according to the different
TSH reference values. Methods: A total of 554 pregnant women, including 509
euthyroid and 45 subclinical hypothyroid (TSH > 3 mIU/L) pregnant women, were
included in this prospective case-controlled study. All pregnant women were in
the third trimester and were TPOAbs negative. Thyroid functions were evaluated
using trimester-specific reference values recommended by the American College
of Obstetrics and Gynecology (ACOG) (TSH > 3 mIU/L) and the American Thyroid
Association (ATA) (TSH ≥ 4 mIU/L) guidelines. Results: Neonatal mortality in
subclinical hypothyroidism with a TSH upper limit of 4 mIU/L was significantly lower
than in the euthyroid group (2 (0.4%) vs 1 (4.5%); p=0.009). There was no significant
difference in terms of adverse maternal and perinatal outcomes in SCH and
euthyroid pregnant women in both TSH reference values. There was no significant
correlation between TSH values and delivery weeks of pregnant women with preterm
delivery (r=0.169, p=0.146). Conclusions: In this study, using different baseline TSH values recommended by the 2020 ACOG and 2017 ATA
guidelines in the third trimester of pregnancy for the diagnosis of subclinical hypothyroidism, it was shown that there was no significant relationship between cases of subclinical hypothyroidism with negative TPOAbs and adverse perinatal outcomes.