Ultrasound Markers of Implantation

Endometrial 3D power Doppler indices change significantly during the normal menstrual cycle. Vascularity indices of the endometrial and subendometrial vessels increase throughout the proliferative phase of the menstrual cycle, reaching a maximum value 2 to 3 days prior to ovulation. From this peak, vascularity indices decrease and reach a nadir 2 to 5 days after ovulation. Reduced endometrial perfusion assessed by 3D power Doppler ultrasound is most likely related to increased uterine contractility. If prolonged, it may cause endometrial hypoxia, leading to detrimental effect on implantation potential. In normal spontaneous menstrual cycles, endometrial vascular indices increase progressively during the course of the luteal phase. Endometrial and subendometrial perfusion is negatively affected by serum estradiol concentrations, which can explain why patients with hyperstimulation have lower endometrial and subendometrial blood flow during the early luteal phase. Our results indicate that 3D power Doppler implantation markers are crucial for planning a single embryo transfer in order to select the most suitable cycle for transfer of a single cryopreserved embryo.