Final answer:
Cord prolapses most frequently occur during the first stage of labor, which is the early part of labor, as the cervix thins and dilates to about 10 cm.
Step-by-step explanation:
Most cord prolapses occur during the first stage of labor, which involves the thinning and dilation of the cervix. This stage is critical for the baby and placenta to be eventually expelled during birth. As the cervix dilates, it reaches about 10 cm to allow the baby to pass through. A cord prolapse may happen if the amniotic membranes rupture before the onset of labor or during the end of the dilation stage due to excessive pressure from the fetal head entering the birth canal. Therefore, cord prolapses are most often associated with the early part of labor rather than the active labor, birth of the baby, or postpartum period.