EVALUATION OF CYCLE-TO-CYCLE VARIATION OF ENDOMETRIAL RESPONSIVENESS USING TRANSVAGINAL SONOGRAPHY IN WOMEN UNDERGOING ASSISTED REPRODUCTION Article O W.-S, So W.W.K., Ng E.H.Y., Ho P.C., Basir G.S. Ultrasound in Obstetrics & Gynecology. John Wiley & Sons. Vol. 19. 2002. P. 484-489