Low-dose aspirin improves endometrial receptivity in the midluteal phase in unexplained recurrent pregnancy loss

Objective To evaluate differences in Doppler parameters and pregnancy outcomes, if any, and to determine the predictive accuracy of such indices, as well as the effects of low-dose aspirin (LDA) in unexplained recurrent pregnancy loss (URPL). Methods An observational study was conducted at Ren Ji Hospital, Shanghai, China, from May 2015 to December 2016. The endometrial thickness, and the pulsatility index (PI), resistive index (RI), and systolic-to-diastolic ratio (S/D) values of endometrial and uterine artery blood flow were collected. Receiver operating characteristic (ROC) curve analysis was used to analyze data from URPL patients (three or more first-trimester spontaneous abortions with unknown etiology) and patients with normal fertility. A second ultrasonography examination was performed in URPL patients who had received daily LDA for 2 months. Results There were 190 URPL patients and 35 control patients. Endometrial thickness was significantly thinner in URPL patients than control patients (P=0.005). The PI, RI, and S/D values for endometrial blood flow and the mean PI, RI, and S/D values for uterine arteries were significantly higher in URPL patients (P<0.001). The predictive accuracy of the indices mentioned above were 0.660, 0.802, 0.852, 0.837, 0.784, 0.929, and 0.929, respectively. Following LDA supplementation, URPL patients showed a significant reduction in resistance to endometrial and uterine artery blood flow (P<0.001). Conclusion URPL patients had impaired uterine perfusion. Doppler parameters are valuable in predicting women at high risk of URPL. LDA could be effective in improving endometrial receptivity.