Once station and rotation are assessed, several prerequisites are met and are listed in Table 29-1. For vacuum extraction, fetuses should also be at least 34 weeks' gestation, and although infrequently used in the United States, fetal scalp blood sampling should not have been recently performed. Of requisites, ascertaining correct head position is essential, and the anatomy of the fetal skull is described in Figure
In unclear cases, sonography is useful to identiy fetal orbits and nasal bridge to aid orientation (Malvasi, 2014).
occiput posterior; OVD operative vaginal delivery.
Regional analgesia or general anesthesia is preferable for low forceps or midpelvic procedures, although pudendal blockade may prove adequate for outlet forceps. As discussed in Chapter 25 (p. 495), regional analgesia during labor does not appear to increase the risk for operative delivery (Halpern, 2004; Marucci, 2007; Wassen, 2014).
The bladder is emptied to provide additional pelvic space and minimize bladder trauma. Urinary retention and bladder dysunction are oten short-term efects offorceps and vacuum deliveries (Mulder, 2012; Pifarotti, 2014). Notably, episiotomy and epidural analgesia, both common associates, are also identified risks for urinary retention. Symptoms are brief and typically resolve with 24 to 48 hours ofpassive Foley catheter bladder drainage.
Biparietal diam.eter = 9.5 cm
Coronal suture --=./
FIGURE 29-1 Fetal head (A, B) at term showing fontanels, sutures, and various dimensions.
There is an increased risk of certain morbidities for both mother and fetus when operative delivery is employed. In general, these are related to the ease with which the delivery is accomplished.
In general, a higher station and/or greater degrees of rotation increase the chance of maternal or fetal injury. Morbidity is most properly compared with morbidity from cesarean delivery, and not with that from spontaneous vaginal delivery. his is the most appropriate comparator because the alternative to indicated operative delivery is cesarean delivery. For example, postpartum wound or uterine infection is more frequent in women following cesarean compared with operative vaginal delivery (Bailit, 2016; Halscott, 2015). Moreover, in a study of more than 1 million births, Spiliopoulos and associates (201i1) reported cesarean delivery, but not operative vaginal delivery, as a risk for peripartum hysterectomy.
he very conditions that lead to indications for operative delivery also increase the need for episiotomy and the likelihood of lacerations (de Leeuw, 2008). That said, forceps and vacuum deliveries are associated with higher rates of third-and fourthdegree lacerations as well s vaginal wall and cervical lacerations (Gurol-Urganci, 2013; Hirayama, 2012; Landy, 2011; Pergialiotis, 2014). These appear to occur more frequently with forceps compared with vacuum extraction, and especially if there is a midline episiotomy (Kudish, 2006; O'Mahony, 2010). Hagadorn-Freathy and coworkers (1991) reported a 13-percent rate of third-and fourth-degree episiotomy extensions and vaginal lacerations for outlet forceps, 22 percent for low forceps with less than 45-degree rotation, 44 percent for low forceps with more than 45-degree rotation, and 37 percent for midforceps deliveries.