The impact of covid-19 on thyroid function tests in pregnancy

Purpose To investigate the effects of laboratory-confirmed SARS-CoV-2 infection on thyroid function tests (TFTs) in pregnant women and to evaluate whether TFT changes are related to the severity and prognosis. Methods Consecutive pregnant women tested for SARS-CoV-2 by RT-PCR at Ankara City Hospital were recruited between January 2021 and September 2021. Thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3), thyroid peroxidase antibody (anti-TPO), and thyroglobulin antibody (anti-TG) were measured on admission. Results Among 747 eligible pregnant women with the same baseline characteristics, 369 RT-PCR-positive women in the patient group and 378 RT-PCR-negative women in the control group were included in the analyses. Pregnant women in the patient group had significantly lower TSH, FT4, FT3, Anti TPO, and Anti TG concentrations compared with those in the control group (p < 0.001). The proportion of patient groups with mild, moderate, severe, and critical diseases were 297 (80.4%), 40 (10.8%), 17 (4.6%), and 15 (4.2%), respectively, among which with the moderate, severe, and critical disease had significantly lower FT3 values (2.5 vs 2.19 pg/mL, p < 0.001) and higher nonthyroidal illness syndrome (NTIS) (29.2 vs. 8.4%, p < 0.001) than those with mild disease. Lower FT3 values increased the risk of ICU admission, NICU admission, and severe disease (p < 0.001). FT3 and TSH correlated positively with lymphocytes (p < 0.001) and negatively correlated with C-reactive protein (CRP) (p < 0.001, p = 0.005). Conclusion The SARS-CoV-2 infection seems to have an impact on the TFTs of pregnant women, and particularly FT3 level seems to be correlated with disease severity.