With a mentum anterior face presentation, forceps can be used to efect vaginal delivery. The blades are applied to the sides of the head along the occipitomental diameter, with the pelvic curve directed toward the neck. Downward traction is exerted until the chin appears under the symphysis. hen, by an upward movement, the face is slowly extracted, with the nose, eyes, brow, and occipur appearing in succession over the anterior margin of the perineum. Forceps should not be applied to the mentum posterior presentation because vaginal delivey is impossible except in vey smal ttuses.
With vacuum delivery, suction is created within a cup placed on the fetal scalp such that traction on the cup aids fetal expulsion. In the United States, vacuum extractor is the preferred term, whereas in Europe it is commonly called a vento use (Fig. 29-16). heoretical beneits of this tool compared with forceps include simpler requirements for precise positioning on the fetal head and avoidance of space-occupying blades within the vagina, thereby mitigating maternal trauma.
Vacuum devices contain a cup, shaft, handle, and vacuum generator. Vacuum cups may be metal or hard or soft plastic, and they may also difer in their shape, size, and reusability. In the United States, nonmetal cups are generally preferred, and there are two main types. he soft cup is a pliable bell-shaped dome, whereas the rigid type has a firm flattened mushroomshaped cup and circular ridge around the cup rim (Table 29-2). When compared, rigid mushroom cups generate significantly more traction force (Hofmeyr, 1990; Muise, 1993). With or positions or with asynclitism, the flatter cup also permits improved placement at the flexion point, which is typically less accessible with these head positions. The trade-of is that the flatter cups have higher scalp laceration rates. Thus, many manufacturers recommend soft bell cups for more straightforward OA deliveries.
Several investigators have compared outcomes with various rigid and soft cups. Metal cups provide higher success rates but greater rates of scalp injuries, including cephalohematomas -�..--A
FIGURE 29-16 Vacuum delivery systems. A. The Kiwi OmniCup contains a handheld vacuum-generating pump, which is attached via flexible tubing to a rigid plastic mushroom cup. B. The Mityvac Mystic II MitySoft Bell Cup has a soft bell cup attached by a semirigid shaft to a handheld pump.
TABLE 29-2. Vacuum Cups for Operative Vaginal Delivery "Reusable cups. bSuitable for occiput posterior positions or asynclitism. (For extractions through a hysterotomy incision during cesarean delivery.
(O'Mahony, 2010). In another study, Kuit and coworkers (1993) found that the only advantage of the soft cups was a lower incidence of scalp injury. hey reported a 14-percent episiotomy extension rate with both rigid and pliable cups. In a review, Vacca (2002) concluded that there were fewer scalp lacerations with the soft cup, but that the rate of cephalohematomas and subgaleal hemorrhage was similar between soft and rigid cups. Importantly, high-pressure vacuum generates large amounts of force regardless of the cup used (Duchon, 1998) .
Aside from the cup, the shaft that connects the cup and handle may be lexible or semiflexible. Tubing-like flexible shafts may be preferred for OP positions or asynclitic presentation to permit better seating of the cup. Last, the vacuum generator may be handheld and actuated by the operator or may be held and operated by an assistant.