After the cervix dilates, if the fetus is in a head-first position, the baby can use its little head to block the cervix, and with the umbilical cord located farther away, the chances of the umbilical cord descending to the cervix are greatly reduced.
For a breech-positioned fetus, it is hard for the baby to use its small buttocks or feet to block the cervix, and may even require the doctor's hand to help block it. There are gaps between the baby's little buttocks and feet, which gives the umbilical cord, already near the baby's lower limbs and buttocks, an opportunity to sneak through.
