Thyroid autoimmunity is associated with increased uterine artery blood flow resistance and predicts adverse pregnancy outcomes in women with unexplained recurrent pregnancy loss: a retrospective cohort study

Background Uterine artery blood flow resistance is critical for endometrial receptivity and successful implantation. Thyroid autoimmunity (TAI) is prevalent in recurrent pregnancy loss (RPL), but whether TAI affects uterine hemodynamics before conception and whether this predicts subsequent pregnancy outcomes has not been directly investigated. Objective This study aimed to determine whether TAI is associated with increased uterine artery resistance in non-pregnant women with unexplained RPL (URPL) and whether elevated resistance indices predict adverse subsequent pregnancy outcomes, thereby providing evidence for preconception risk stratification. Methods A total of 486 non-pregnant women with URPL were enrolled in this retrospective cohort study. Serum TPOAb, TGAb, TSH, FT4 and FT3 were measured. TAI and non-TAI, based on their thyroid antibody status. TAI was defined as TPOAb ≥60IU/mL and/or TGAb ≥60 IU/mL. All underwent transvaginal Doppler ultrasound to measure bilateral uterine artery resistance index (RI), pulsatility index (PI), and peak systolic velocity/end diastolic velocity (S/D). We assessed the incidence of pregnancy, subsequent pregnancy loss, and live birth. Logistic regression analysis was performed to examine the associations between TAI, uterine artery blood flow parameters and subsequent pregnancy loss. Results TAI women (n=242) had significantly higher RI, PI and S/D values compared with non-TAI women (n=244) (left RI: 0.82[0.77, 0.85] vs. 0.77 [0.73, 0.83], P Conclusion Thyroid autoimmunity is associated with increased uterine artery blood flow resistance in non-pregnant URPL women. TAI positivity and elevated uterine artery Doppler indices (mean RI, PI and S/D) were independently associated with subsequent pregnancy loss.