Approximately 2 to 10 percent of singleton term cephalic fetuses deliver in an occiput posterior (OP) position (Cheng, 2010). Many fetuses delivering OP are OA in early labor and relect malrotation during labor. Predisposing risks include epidural analgesia, nulliparity, greater fetal weight, and prior delivery with OP positioning (Cheng, 2006a; Gardberg, 2004; Lieberman, 2005). Regarding pelvic shape, an anthropoid pelvis and narrow subpubic angle can predispose (Barth, 2015; Ghi, 2016).
Women with a persistent OP position have higher associated rates of prolonged second-stage labor, cesarean delivery, and operative vaginal delivery. For women who deliver vaginally, rates of blood loss and of third-and fourth-degree lacerations are increased (Senecal, 2005).
plication rates then those born positioned OA. Cheng and coworkers (2006b) compared outcomes of 2591 women under going delivery with a persistent OP position with those of28,801 women whose newborns were delivered OA. Virtually every possible delivery complication was found more frequently with persistent OP position. Only 46 percent of these women deliv ered spontaneously, and the remainder accounted for 9 percent of cesarean deliveries performed. hese investigators also found that an OP position at delivery was associated with more adverse cord gases, birth trauma, Apgar scores <7, and intensive care nursery admission, among others. Similar results were reported by Ponkey (2003) and Fitzpatrick (2001) and their associates.
Methods to prevent persistent OP position and its associated morbidity have been investigated. First, digital examination for identiication of fetal head position can be inaccurate, and transabdominal sonography can be used to increase accuracy (Dupuis, 2005; Zahalka, 2005). The transducer is placed transversely just cephalad to the maternal mons pubis. In the sonogram, fetal orbits and nasal bridge lie ventrally, whereas the occiput apposes the lower sacrum. Such information may provide an explanation for prolonged second-stage labor or may identiy suitable candidates for rotation. Of other possible interventions, varying maternal position either antepartum or during labor does not appear to lower rates of persistent OP position (Desbriere, 2013; Kariminia, 2004; Le Ray, 2016).
The fetus in an OP position may be delivered either spontaneously or by operative vaginal delivery. First, if the bony pelvic outlet is roomy and the perineum is somewhat relaxed from prior deliveries, rapid spontaneous OP delivery will often take place. Conversely, if the perineum is resistant to stretch, secondstage labor may be appreciably prolonged. During each expulsive efort, the head is driven against the perineum to a much greater degree than when the head position is OA. This leads to greater rates of third-and fourth-degree lacerations (Groutz, 2011; Melamed, 2013).
In some cases, spontaneous vaginal delivery from an OP position does not appear feasible or expedited delivery is needed. Here, manual rotation with spontaneous delivery from an OA position may be preferred. This technique is described fully in Chapter 29 (p. 560). Successful rotation rates range from 47 to 90 percent. And, as would be expected, lower rates of cesarean delivery, vaginal laceration, and maternal blood loss follow rotation to OA position and vaginal delivery (Le Ray, 2005; Sen, 2013; Shafer, 2006, 2011). Disadvantageously, manual rotation is linked with higher cervical laceration rates. Thus, careful inspection of the cervix following rotation is mandatory.