presentation, in childbirth, the position of the fetus at the time of delivery. The presenting part is the part of the fetus that can be touched by the obstetrician when he probes with his finger through the opening in the cervix, the outermost portion of the uterus, which projects into the vagina. In nearly all deliveries the presenting part is the vertex, the top of the head; in 3 or 4 percent of deliveries, it is the breech (buttocks). Face presentation and transverse (cross) presentation are rare.
In vertex presentations the head of the fetus most commonly faces to the right and slightly to the rear. This position is said to be the most usual one because the fetus is thus best accommodated to the shape of the uterus. In breech presentation the buttocks or the legs are the first to pass through the pelvis. The feet may be alongside the buttocks, or the legs may be extended against the face. Because the head is the last part of the fetus to be delivered in breech birth, there is some danger that the fetus will be asphyxiated; there is also danger that the umbilical cord will be compressed during birth of the head. In face presentation it may be necessary to turn the fetus before delivery if the chin is directed backward. Transverse presentation, which occurs only once in several hundred labours, requires turning of the fetus before vaginal delivery or else delivery by cesarean section.