Objective:To evaluate the morphological structure of the female pelvic hiatus(PH)in the late pregnancy by transvaginal three-dimensional ultrasound. Methods:Fifty cases of cesarean section delivery and 50 cases of vaginal delivery discharged from the hospital from January 2012 to December 2014 were taken as cesarean section group and vaginal delivery group and were checked by transvaginal three-dimensional ultrasound. Fifty cases of nulliparous women with gynecological diseases examination in the same period were taken as control group. Ultrasound findings of normal PH and PH after delivery were observed. The variation characteristics of PH left and right diameter

front back diameter and area between two different delivery methods in different time points were compared. Results:(1) PH morphology in control group was in diamond-shaped fissure structure;PH morphology of cesarean section group after delivery was consistent with that of control group(24 cases/48 cases)

and the PH morphology of the remaining 26 cases was fuzzy in structure with echo disorder.(2)PH left-right diameter

anteroposterior diameter and area at the prenatal resting state

anal contraction movement

and Valsalva maneuver were higher in cesarean section delivery group and vaginal delivery group than in control group(P<0.05). In cesarean section delivery group

the above indexes were lower at 6 weeks and 3 months after delivery than before delivery(P<0.05). In vaginal delivery group

the above indexes were increased after delivery and were decreased from the 3 rd month after delivery;the above indexes were higher in vaginal delivery group after delivery than in vaginal delivery group before delivery

cesarean section delivery group

and control group(P <0.05). Conclusion:Three dimensional ultrasound can clearly observe the female pelvic floor structure.Both delivery modes exert effect on the female pelvic diaphragm hiatus;the effect of the vaginal delivery is more significant.