After taking written informed consent, all patients recruited in the study will undergo, detailed medical history and complete clinical examination will be obtained along with necessary laboratory investigations and ultrasound findings The standard protocol of the Assisted Reproduction unit in Ain Shams University Maternity Hospital for induction of ovulation in ICSI patients which it is the long protocol will be given for all patients in the study. Endometrial and sub-endometrial blood flow for every patient in the 3 groups will be assessed by transvaginal ultrasound using Medison Sonoace R5 ultrasound machine, eight hours before giving the trigger, after they have completely emptied their bladders (2D power Doppler will be performed). This will be repeated one week after the day of embryo transfer. Endometrial blood flow will be detected by intra-endometrial or the adjacent sub-endometrial regions within 10 mm of the echogenic endometrial borders. Double thickness of the endometrium will be measured (maximum distance between each myometrial/endometrial interface through the longitudinal axis of the uterus). The pulsatility index (PI) and resistance index (RI) of the endometrial arteries will be calculated. Analysis will be used together with computer algorithms to form indices of blood flow within the endometrium. The parameters will be analyzed by software for: (i) resistance index (RI): the difference between maximal systolic blood flow and minimal diastolic flow divided by the peak systolic flow (S-D/S); (ii) pulsatility index (PI): the difference between maximal systolic blood flow and minimal diastolic flow divided by the mean flow throughout the cycle (S - D/mean); (iii) the ratio between peak systolic flow and lowest diastolic flow (S/D). These three parameters express the resistance to flow from the point of measurement downstream. The patients will be divided into three groups according to the condition of the endometrial blood flow: In Group 1, no endometrial blood flow is detected; Group 2 has sub-endometrial blood flow detected, and Group 3 has both endometrial and sub-endometrial blood flow detected.