As this allows for a much more rapid vaginal birth, there is an increased risk of tearing of the perineal soft tissues. At the time of delivery, the strong uterine contractions and maternal bearing down almost instantly overwhelm the integrity of a previously unstretched vaginal orifice.
This facilitates a quicker vaginal birth, but it also increases the risk of tearing in the perineal soft tissues. During delivery, strong uterine contractions and maternal effort quickly compromise the integrity of a previously unstretched vaginal opening.