By the time of perineal distention, 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. 426). In most cases, position is directly occiput anterior (OA) or is rotated slightly oblique. But, in perhaps 5 percent, occiput posterior (OP) positioning persists.
With each contraction, the vulvovaginal opening is dilated by the fetal head to gradually form an ovoid and inally, an almost circular opening (Fig. 27-1). his encirclement of the largest head diameter by the vulvar ring is termed crowning. he perineum thins and may spontaneously lacerate. he anus becomes greatly stretched, and the anterior wall of the rectum can easily be seen through it.
Routine episiotomy is no longer recommended, and selective use aims to enlarge the vaginal opening for specific indications (p. 529). To limit spontaneous vaginal laceration, some perform antenatal massage of the perineal body to increase perineal distensibility or intrapartum perineal massage to widen the introitus for head passage. During massage with a lubricant, the perineum is grasped in the midline by both hands using the thumb and opposing ingers. Outward and lateral stretching to thin the perineum is repeatedly performed. But in randomized studies, this technique did not significantly prevent perineal laceration (Beckmann, 2013; Mei-dan, 2008; Stamp, 2001). Antepartum use of the Epi-No intravaginal pump balloon has a similar aim, but it also fails to prevent perineal trauma or levator injury (Brito, 2015; Kamisan Atan, 2016).
When the head distends the vulva and perineum enough to open the vaginal introitus to a diameter of 5 cm or more, a gloved hand may be used to support the perineum (Fig. 27-2). he other hand is used to guide and control the fetal head to deliver the smallest head diameter through the introitus and to
FIGURE 27-2 Delivery of the head. The mouth appears over the perineum.
avoid expulsive delivery. Slow delivery of the head may decrease lacerations (Laine, 2008). Overall, bracing the perineum lowers rates of anal sphincter injury compared with a "hands of' approach to delivery (Bulchandani, 2015; McCandlish, 1998).
Alternatively, if expulsive eforts are inadequate or expeditious delivery is needed, the modied Ritgen maneuvermay be employed or an episiotomy cut. With the modified maneuver, gloved ingers beneath a draped towel exert forward pressure on the fetal chin through the perineum just in front of the coccyx. Concurrently, the other hand presses against the occiput (Fig. 27-3). Originally described in 1855, the maneuver allows controlled fetal head delivery (Cunningham, 2008). It also favors neck extension so that the head passes through the introitus and over the perineum with its smallest diameters. Comparing the Ritgen maneuver with simple perineal support in 1623 women, Jonsson and colleagues (2008) found a similar incidence of third-and fourth-degree tears, defined later (p. 528).
FIGURE 27-1 Perineum is supported as the head crowns.
FIGURE 27-3 Modified Ritgen maneuver. Moderate upward pressure is applied to the fetal chin by the posterior hand covered by a sterile towel. The other hand applies occipital pressure.
• Delivery of the Shoulders