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 <0.001; right RI: 0.82[0.77, 0.85] vs. 0.78 [0.73, 0.84], P <0.001; Right PI: 2.36[2.19, 2.59] vs. 2.29[1.89, 2.56], P = 0.010; Left S/D: 5.56[4.00, 6.25] vs. 4.35[3.70, 5.88], P <0.001; Right S/D: 5.56[4.35, 6.67] vs. 4.55[3.70, 6.25], P <0.001). During follow-up, 240 of 486 women achieved a next pregnancy (49.3%). The clinical pregnancy rate did not differ significantly between the TAI and non-TAI groups (42.6% vs. 48.0%, P = 0.379). Among those who conceived, TAI women had a significantly higher rate of recurrent pregnancy loss (28.7% vs. 16.0%) and a lower live birth rate (71.3% vs. 84.0%) (P = 0.018). Logistic regression showed that TAI positivity (aOR=2.02, 95%CI 1.08-3.87), mean RI (aOR=1.96, 95%CI 1.3-3.00), mean PI (aOR=2.24, 95%CI 1.58-3.30), and mean S/D (aOR=3.567, 95%CI 1.03-1.90) were independent predictors of subsequent pregnancy loss. 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.