Little is known about the anatomic and physiologic changes in the pelvic floor that occur during pregnancy. The purpose of this study was to prospectively document pelvic organ support throughout pregnancy using the standardized system of the International Continence Society, also known as the Pelvic Organ Prolapse Quantification (POPQ) Staging System. Pelvic organ support evaluations were performed in nulliparous pregnant women presenting for routine obstetric care during each trimester. POPQ stage assignments and POPQ component measurements were compared for first-, second- and third-trimester examinations. Overall POPQ stage was significantly higher in the third trimester than in the first (P=0.001). Individual POPQ points which showed significant differences between the first and third trimesters include Aa, PB, Ap, Ba, Bp, TVL and GH. These findings probably represent normal physiologic changes of the pelvic floor during pregnancy, but suggest that significant changes may be objectively demonstrated prior to delivery.