When the fetal head is about to be delivered through the vagina, the fetal head continues to descend, compressing the vaginal opening and surrounding tissues, and local swelling, thinning or even shine can be seen. At this time, if the perineum is not protected, not only the perineum may be torn, but it may even be torn all the way to the anus. When the fetal head is about to be delivered, medical staff must pay attention to one important thing during delivery.