To study the effect of child birth on pelvic organ mobility in a prospective observational study. A total of 200 women were recruited early in their first ongoing pregnancy and examined by translabial ultrasound in the first/early second trimester, the late third trimester, and 2–5 months postpartum. Peripartal changes in the mobility of urethra, bladder, cervix, and rectal ampulla were correlated with labor and delivery data. A total of 169 women returned postpartum (84.5%). Highly significant increases in organ mobility on Valsalva were found after vaginal delivery (P < .001), with forceps causing the most marked changes. Length of second stage, especially active second stage, correlated with an increase in pelvic organ descent (P = .03 to P < .001). The influence of gestational age, length of first stage, and birth weight did not reach significance. Vaginal birth, in particular operative delivery, negatively affects pelvic organ support. This appears to be true for all three vaginal compartments. All forms of cesarean delivery were associated with relatively less pelvic organ descent. These findings may partly explain the protective effect of elective cesarean delivery for future symptoms of pelvic floor disorders.