The natural culmination of second-stage labor is controlled vaginal delivery of a healthy neonate with minimal trauma to the mother. Although some clinical settings favor cesarean delivery, for most fetuses, vaginal birth is preferred. For the mother, spontaneous vaginal vertex delivery poses the lowest risk of most maternal comorbidity, and comparisons with cesarean delivery are found in Chapter 30 (p. 548). Delivery is usually spontaneous, although some maternal or fetal complications may warrant operative vaginal delivery, described in Chapter 29 (p. 533). Last, a malpresenting fetus or multifetal gestation in many cases may be delivered vaginally but requires special techniques. These are described in Chapters 28 and 48.
The end of second-stage labor is heralded as the perineum begins to bulge, and the fetal scalp is seen through the separating labia. Perineal pressure from the fetal head creates reflexive pushing efforts. At this time, additional staff to attend the neonate and instruments are readied for delivery. Fetal heart rate monitoring continues. As one example, a nuchal cord often tightens with fetal descent and may lead to deepening variable decelerations. If the bladder is distended, catheterization can provide added pelvic space.
During second-stage labor, pushing positions may vary. But for delivery, the dorsal lithotomy position is most common and often the most satisfactory. Leg holders or stirrups are often used to assist. With or without their use, perineal laceration rates were equal in one randomized study of 214 parturients (Corton, 2012). With positioning, legs are not separated too widely or placed one higher than the other. Legs are not strapped into the stirrups. This permits quick flexion of the thighs backward onto the abdomen should shoulder dystocia develop. Legs may cramp during second-stage pushing, and cramping can be relieved by creating gentle muscle stretch, by brief massage, or both.
Preparation for delivery includes vulvar and perineal cleansing. If desired, sterile drapes are placed to cover the legs and abdomen and expose only the perineum. Scrubbing, gowning, gloving, and donning protective mask and eyewear protect both the gravida and accoucheur from infectious agents.
By the end of second-stage labor, the position of the occiput is usually known. In some cases, however, molding and caput formation may have precluded early accurate identification. At this time, careful assessment is again performed as described in Chapter 22 (p. 429). In most cases, position is occiput anterior (OA) or is rotated slightly oblique. But, in perhaps 5 percent, an occiput posterior (OP) position persists.
With each contraction, the vulvovaginal opening is dilated by the fetal head to gradually form an ovoid and finally, an almost circular opening. This encirclement of the largest head diameter by the vulvar ring is termed crowning. The anus becomes greatly stretched, and the anterior wall of the rectum ...