In some pregnancies, the placenta may develop at an abnormal location or may extensively invade the adjacent myometrium. Clinical entities include placenta previa, in which trophoblastic cells implant over or near the internal cervical os (Fig. 27-1). In other cases, trophoblast aggressively burrows into the myometrium. Depending on the invasion depth, placenta accreta, placenta increta, or placenta percreta is diagnosed (Fig. 27-2). The term placenta accrete syndromes is clinically useful to summarize these three types and is used here and throughout the text. Another interchangeable phrase also often used is morbidly adherent placenta (Bailit, 2015; Silver, 2015a).
FIGURE 27-2
Placenta accrete syndromes. A. Placenta accreta: villi are attached to myometrium. B. Placenta increta: villi have invaded the myometrium. C. Placenta percreta: villi have penetrated through the myometrium and serosa. (Reproduced with permission from Cunningham FG, Leveno KJ, Bloom SL, et al (eds): Obstetrical hemorrhage. In Williams Obstetrics, 24th ed. New York, McGraw-Hill Education, 2014.)
For the gravida and her newborn, catastrophic sequelae can result from abnormal placental implantation. Of these, obstetric hemorrhage, cesarean hysterectomy, preterm delivery, and their attendant complications are prominent. Worryingly, rates of both placenta previa and accrete syndromes are rising. Most of this trend in the United States derives from the current substantial cesarean delivery rate, which is a known risk factor for both (Chap. 25, p. 404). Early identification and preparation can mitigate several of the associated complications. This chapter emphasizes many of these preventive steps.
In understanding the pathophysiology and management of placental disorders, one key concept is the mechanism by which hemostasis is achieved after normal delivery. First, recall that an incredible volume of blood flows through the intervillous space near term. Accurately measuring uteroplacental blood flow is challenging, and simultaneous calculation of uterine, ovarian, and collateral vessel contributions is currently not technically possible. This limitation stands even if the orthogonal capabilities of magnetic resonance angiography are used (Pates, 2010). With indirect methods that include clearance rates of androstenedione and xenon-133, uteroplacental blood flow has been calculated to increase progressively throughout pregnancy. Estimates at term range from 450 to 600 mL/min (Edman, 1981; Kauppila, 1980). These values are similar to those obtained with invasive methods—500 to 750 mL/min (Assali, 1953; Browne, 1953; Metcalfe, 1955). To put this remarkable rate of blood flow into context, remember that the entire cardiac output of a nonpregnant woman approximates only 3500 mL/min.
This prodigious flow circulates through the spiral arteries, which average 100 to 120 in number. These vessels have no muscular layer because of early endotrophoblastic remodeling. This placental structure creates a low-pressure system. With placental separation, these vessels at the implantation site are avulsed, and hemostasis is achieved first by myometrial contractions, which compress this formidable number of relatively large vessels. Notably, in the normal lower uterine segment, this muscle cell population is diminished. Throughout the uterus, contraction is followed by clotting and obliteration of vessel lumens. Thus, after delivery, the myometrium within and adjacent to the denuded implantation site normally contracts vigorously, and hemorrhage from the implantation site is forestalled. Importantly, an intact coagulation system is not necessary for postpartum hemostasis unless there are lacerations in the uterus, birth canal, or perineum. Conversely, massive hemorrhage can result despite normal coagulation if the placenta is abnormally implanted into the inactive lower uterine segment as with placenta previa. In these cases, the paucity of myometrial cells that would normally contract and encircle the spiral vessels explains this bleeding. In addition, if placental tissue has attached to or grown into the myometrium, as with placenta accrete syndromes, then hemostasis at the implantation site is further impaired.
The Latin previa means going before—and in this sense, the placenta goes before the fetus into the birth canal. In obstetrics, placenta previa describes a placenta that is implanted somewhere in the lower uterine segment, either over or very near the internal cervical os. Because these anatomic relationships cannot always be precisely defined, and because they frequently evolve across pregnancy, terminology can sometimes be confusing, as discussed subsequently.
Placenta previas diagnosed early in pregnancy may not persist as gestation advances. In earlier literature, the term placental migration was used to describe the apparent movement of the placenta away from the internal os (King, 1973). Migration is clearly a misnomer because decidual invasion by chorionic villi on either side of the cervical os persists. Although it is obvious that the placenta does not move per se, the mechanism of apparent movement is not completely understood. Several explanations are likely additive.
First, apparent movement of the low-lying placenta relative to the internal os may simply reflect the imprecision of two-dimensional sonography to clearly define this relationship. Second, the lower and upper uterine segments do grow at differing rates as pregnancy progresses (Becker, 2001). The upper uterus establishes greater blood flow, and placental growth, supported by this enhanced supply, favors the fundus. The term trophotropism describes this event. Thus, many of the placentas that “migrate” most likely never were circumferentially implanted with true villous invasion that reached the internal cervical os. And, their apparent exodus results from preferential fundal geographic growth.
Placental migration has been quantified in several studies. Sanderson and Milton (1991) studied 4300 women at midpregnancy and found that 12 percent had a low-lying placenta. Of those not covering the internal os, previa did not persist, and none subsequently had placenta-associated hemorrhage. Conversely, approximately 40 percent of placentas that covered the os at midpregnancy continued to do so until delivery. Thus, placentas that lie close to but not over the internal os at a gestational age up to the early third trimester are unlikely to persist as a previa by term (Dashe, 2002; Heller, 2014; Parrott, 2015; Robinson, 2012). Still, Bohrer and associates (2012) reported that a second-trimester low-lying placenta was associated with antepartum admission for hemorrhage and increased blood loss at delivery.
The likelihood that placenta previa persists after being identified sonographically at given epochs before 28 weeks’ gestation is shown in Figure 27-3. Similar findings for twin pregnancies are reported until 23 weeks’ gestation. At later ages, the previa persistence rate is much higher (Kohari, 2012). Also from the figure, the effects of a prior cesarean delivery are obvious, and placenta previa is less likely to “migrate” within a uterus with a prior cesarean hysterotomy scar.
FIGURE 27-3
Likelihood of placenta previa or low-lying placenta persistence at delivery. Data points reflect the sonographic diagnosis at three pregnancy epochs of a previa or placental edges lying 1 to 5 mm from the cervical internal os. (Reproduced with permission from Cunningham FG, Leveno KJ, Bloom SL, et al (eds): Obstetrical hemorrhage. In Williams Obstetrics, 24th ed. New York, McGraw-Hill Education, 2014; data from Oyelese, 2006).
Terminology for placenta previa has been confusing. In a recent Fetal Imaging Workshop sponsored by the National Institutes of Health (Reddy, 2014), the following classification was recommended (Table 27-1):
| Placenta previa: the internal os is covered completely or partially by placenta |
| Low-lying placenta: implantation in the lower uterine segment is such that the placental edge does not reach the internal os but is within 2 cm of it |
| Discarded term: marginal previa described a placenta that was at the edge of the internal os but did not overlie it |
Placenta previa—the internal os is covered completely or partially by placenta (see Fig. 27-1 and Fig. 27-4). In the past, these were further classified as either a total or partial previa.
Low-lying placenta—implantation in the lower uterine segment is such that the placental edge does not reach the internal os but is within 2 cm from it. The discarded term marginal previa described a placenta that was at the edge of the internal os but did not overlie it.
FIGURE 27-4
Second-trimester placenta previa. On speculum examination, the cervix is 3- to 4-cm dilated. The arrow points to mucus dripping from the cervix. (Photographs used with permission from Dr. Kelley S. Carrick. Reproduced with permission from Cunningham FG, Leveno KJ, Bloom SL, et al (eds): Obstetrical hemorrhage. In Williams Obstetrics, 24th ed. New York, McGraw-Hill Education, 2014.)
Clearly, the classification of some cases of previa will depend on cervical dilatation at the time of assessment (Dashe, 2013; Reddy, 2014). For example, a low-lying placenta and a cervical dilatation of 2 cm may become a placenta previa at 4-cm dilatation because the cervix has dilated to expose the placental edge (see Fig. 27-4). Conversely, a total placenta previa before cervical dilatation may become partial at 4-cm dilatation because the cervical opening now extends beyond the edge of the placenta. Digital palpation in an attempt to ascertain these changing relations between the placental edge and internal os as the cervix dilates usually causes severe hemorrhage and is generally avoided!
With any degree of placenta previa, a certain element of spontaneous placental separation is an inevitable consequence of lower uterine segment remodeling and cervical dilatation. Although this frequently causes bleeding, and thus technically constitutes a placental abruption, this term is usually not applied in these instances.
Somewhat but not always related is vasa previa. With this condition, fetal vessels course through the placental membranes and lie across the cervical os (Bronsteen, 2013). Antepartum treatment of vasa previa is discussed in Chapter 16 (p. 271).
The reported incidence for placenta previa in the United States is 1 case per 200 to 300 deliveries (Martin, 2005; Silver, 2015a). The frequency at Parkland Hospital from 1988 through 2011 was approximately 1 in 470 for 209,020 singleton births (Wortman, 2015). Similar frequencies have been reported from Canada, England, Finland, and Israel (Crane, 1999; Gurol-Urganci, 2011; Räisänen, 2014; Rosenberg, 2011). The incidence from a Japanese study was unusually low at only 1 in 700 deliveries (Matsuda, 2011). Except for the last study, these reported frequencies are remarkably similar considering the lack of precision in definition and classification discussed above.
Several factors increase the risk for placenta previa (Table 27-2). One of these—multifetal gestation—seems intuitive because of the larger total placental surface area. And indeed, the incidence of associated previa with twin pregnancy is increased by 30 to 40 percent compared with that of singletons (Ananth, 2003a; Weis, 2012). Many of the other associated factors are less intuitive.
The frequency of placenta previa increases with maternal age (Biro, 2012). At Parkland Hospital, this incidence increased from a low rate of approximately 1 in 1660 for women 19 years or younger to almost 1 in 100 for women older than 35 (Fig. 27-5). Also, coincidental with increasing maternal age in the United States and Australia, the overall incidence of previa has increased substantively (Frederiksen, 1999; Roberts, 2012). The FASTER Trial, which included more than 36,000 women, cited the frequency of previa to be 0.5 percent for women <35 years compared with 1.1 percent in those >35 years (Cleary-Goldman, 2005).
The risk for previa increases with parity (Räisänen, 2014). The obvious effects of advancing maternal age and parity can be confounding. Still, Babinszki and colleagues (1999) reported that the 2.2-percent incidence in women with parity of five or greater was increased significantly compared with that of women with lower parity. Alternatively, there seems to be no relationship to interpregnancy intervals (Fox, 2015).
Women who have undergone one or more cesarean deliveries are at greater risk for subsequent placental disorders that include placenta previa, abruption, or accrete syndromes (Klar, 2014). The cumulative risks for placenta previa that accrue with the increasing number of cesarean deliveries are extraordinary. In a Network study of 30,132 women undergoing cesarean delivery, Silver and associates (2006) reported an incidence of 1.3 percent for those with only one prior cesarean delivery, but it was 3.4 percent if there were six or more prior cesarean deliveries. In a retrospective cohort of nearly 400,000 women who were delivered of two consecutive singletons, those with a cesarean delivery for the first pregnancy had a significant 1.6-fold increased risk for previa in the second pregnancy (Gurol-Urganci, 2011). These same investigators reported a 1.5-fold increased risk from six similar population-based cohort studies. Gesteland (2004) and Gilliam (2002) and their coworkers calculated that the likelihood of previa was increased more than eightfold in women with parity greater than four and who had more than four prior cesarean deliveries.
In addition, the circumstances of the prior delivery may have implications. For example, Downes and associates (2015) found a higher previa rate in a second pregnancy if the cesarean delivery in the preceding pregnancy was performed prior to labor compared with those performed intrapartum. Moreover, a higher inherent rate of recurrence is seen in women with a prior placenta previa that did not require hysterectomy. Recurrence rates range from 2 to 5 percent (Gorodeski, 1981; Rasmussen, 2000; Roberts, 2012).
Importantly, women with a prior uterine incision and current placenta previa have an increased likelihood that cesarean hysterectomy will be necessary for hemostasis because of an associated accrete syndrome (Wei, 2014). This is discussed in further detail on page 442. In the study by Frederiksen and colleagues (1999), 6 percent of women who had a primary cesarean delivery for previa required a hysterectomy. This rate was 25 percent for women with a previa undergoing repeat cesarean delivery.
As an associated correlate, some evidence supports a greater risk of placenta previa as the number of surgical pregnancy terminations accrues (Barrett, 1981; Faiz, 2003). This relationship is strongest for women specifically with prior curettage (Johnson, 2003).
The relative risk of placenta previa is increased at least twofold in women who smoke cigarettes (Ananth, 2003a; Usta, 2005). It has been postulated that carbon monoxide hypoxemia causes compensatory placental hypertrophy and greater surface area. Alternatively, smoking may be related to decidual vasculopathy that has been implicated in the genesis of previa.
Women who have otherwise unexplained abnormally elevated prenatal screening levels of maternal serum alpha-fetoprotein (MSAFP) are at increased risk for previa and a host of other abnormalities. Moreover, women with a previa who also have an MSAFP level ≥2.0 multiples of the median (MoM) at 16 weeks’ gestation are at increased risk for late-pregnancy bleeding and preterm birth.
Painless bleeding is the most characteristic event with placenta previa. Bleeding usually does not appear until near the end of the second trimester or later, but it can begin even before midpregnancy. Undoubtedly, some late abortions are caused by an abnormally located placenta.
Bleeding from a previa usually begins without warning and without pain or contractions in a woman who has had an uneventful prenatal course. This so-called sentinel bleed is rarely so profuse as to prove fatal. Usually it ceases, only to recur. In perhaps 10 percent of women, particularly those with a placenta implanted near but not over the cervical os, there is no bleeding until labor onset. Bleeding at this time varies from slight to profuse, and it may clinically mimic placental abruption.
A specific sequence of events leads to bleeding in cases in which the placenta is located over the internal os. First, the uterine body remodels in labor to form the lower uterine segment. With this, the internal os dilates, and some of the implanted placenta inevitably separates. Bleeding that ensues is augmented by the inherent inability of myometrial fibers in the lower uterine segment to contract and thereby constrict avulsed vessels.
As well as placenta location, cervical effacement has been shown by some to increase the incidence of bleeding with a placenta previa. Stafford and coworkers (2010), but not Trudell and colleagues (2013), found that a previa and a third-trimester cervical length <30 mm increased the risk for hemorrhage, uterine activity, and preterm birth. Friszer and associates (2013) showed that women admitted for bleeding had a greater chance of delivery within 7 days if the cervix was <25 mm. However, Trudell and colleagues (2013) did not confirm this.
In addition to antepartum bleeding, blood loss from the lower segment implantation site also frequently continues after placental delivery during cesarean delivery. There may also be lacerations in the friable cervix and lower segment. The latter may be especially problematic following manual removal of a somewhat adhered placenta.
A frequent and serious complication associated with placenta previa arises from its abnormally firm placental attachment. This is anticipated because of poorly developed decidua that lines the lower uterine segment. Biswas and coworkers (1999) performed placental bed biopsies in 50 women with a previa and in 50 control women. Trophoblastic giant-cell infiltration of spiral arterioles—rather than endovascular trophoblast—was found in half of previa specimens, but in only 20 percent from those with normally implanted placentas.
Some of these women have pathologically abnormal ingrowth of placental tissue into the myometrium (Fig. 27-6). Placenta accrete syndromes arise from abnormal placental implantation and adherence and are classified according to the depth of placental ingrowth into the uterine wall. These include placenta accreta, increta, and percreta, which are discussed in detail on page 442. In a study of 514 cases of previa reported by Frederiksen and associates (1999), abnormal placental attachment was identified in 7 percent. As discussed above, previa overlying a prior cesarean incision conveys a particularly high risk for morbidly adherent placenta.
FIGURE 27-6
This cesarean hysterectomy specimen has been bisected and opened to show the placenta (bracket) overlying the cervix. The dotted line demarcates the fetal surface of the placenta previa. In this previa case, the placenta invades up to the uterine serosa on the left (arrowheads) and through the serosa on the right (arrow).
Placenta previa is rarely complicated by coagulopathy even when the placenta is extensively separated from its implantation site (Wing, 1996b). Placental thromboplastin, which incites the intravascular coagulation seen with placental abruption, is presumed to readily escape through the cervical canal rather than be forced into the maternal circulation (Cunningham, 2015). The paucity of large myometrial veins in this area may also be somewhat protective.
Whenever uterine bleeding is noted after midpregnancy, placenta previa or abruption should always be considered. In the Canadian Perinatal Network study, placenta previa accounted for 21 percent of women admitted from 22 to 28 weeks’ gestation with vaginal bleeding (Sabourin, 2012). Previa should not be excluded until sonographic evaluation has clearly proved its absence. If necessary, diagnosis by clinical examination is done using the double set-up technique because it requires that a finger be passed through the cervix and the placenta palpated. Fortunately, this is rarely indicated because placental location can almost always be ascertained sonographically. If this cannot be done, then a digital examination should not be performed unless delivery is planned. A cervical digital examination is done with the woman in an operating room and with preparations for immediate cesarean delivery because even the gentlest examination can cause torrential hemorrhage.
Evaluation of placental location is a standard component of the routine obstetric sonographic examination (American Institute of Ultrasound in Medicine, 2013). This is usually accomplished with transabdominal sonography. If the placenta clearly either overlies the cervix or in contrast lies distant from the lower uterine segment, the examination has excellent sensitivity and negative predictive value (Olive, 2006, Quant, 2014). If a question remains regarding the relationship between the inferior placental edge and the internal cervical os, transvaginal sonography is the most accurate method of assessment (Fig. 27-7). This approach is considered safe, even in the presence of bleeding. Translabial sonography is less commonly used, but it may be of benefit if transabdominal images are suboptimal and transvaginal sonography is not available.
FIGURE 27-7
Placenta previa. A. In this transvaginal image at 34 weeks’ gestation, the anterior placenta completely covers the internal cervical os. The internal os and endocervical canal are marked by arrows. B. This transvaginal image at 34 weeks’ gestation depicts a posterior placenta that just reaches the level of the internal cervical os (arrow). The endocervical canal is marked by arrowheads. Whether the placenta partially covers the closed os or just reaches the margin of the os is not considered a distinction that is technically discernible or clinically helpful. (Used with permission from Dr. Jodi Dashe.)
Sonography can be used to exclude a placenta previa with a high negative predictive value at any gestational age (Reddy, 2014). And quick and accurate localization can be accomplished using standard sonographic techniques (Dashe, 2013). In many cases, transabdominal sonography alone is confirmatory. In some women, however, maternal habitus may limit visualization of the lower uterine segment. Moreover, sometimes a large fundal placenta is not appreciated to extend down to the internal cervical os. Also, a full bladder may artificially elongate the cervix and give the impression that placenta overlies it. Therefore, doubtful cases should be confirmed after bladder emptying. Transvaginal sonography is safe, and the results are superior to abdominal sonography. For example, in a comparative study by Farine and associates (1988), the internal os was visualized in all cases using transvaginal sonography but was seen in only 70 percent using transabdominal sonography.
Placenta previa is diagnosed when the placenta covers or just reaches the internal cervical os. In the absence of any other indication, sonography need not be frequently repeated simply to document placental position. Instead, a second sonographic assessment is recommended at approximately 32 weeks’ gestation to evaluate for resolution of the previa (Reddy, 2014; Silver, 2015a). If the previa persists, additional transvaginal sonography is then recommended at 36 weeks’ gestation.
A low-lying placenta is diagnosed if the placental edge is <2 cm from the internal os, but not covering it (Fig. 27-8). With addition indications, a second sonographic evaluation is scheduled for 32 weeks’ gestation. At this time, if the placental edge now is still <2 cm from the internal os, then transvaginal sonography is repeated at 36 weeks. Importantly, in cases of resolved placenta previa or low-lying placenta, localization of the umbilical cord insertion is necessary because these pregnancies are at risk for vasa previa.
FIGURE 27-8
Low-lying placenta. In this transvaginal image at 34 weeks’ gestation, the measurement from the inferior edge of the posterior placenta (long arrow) to the internal os (arrowhead) is approximately 1 cm. The endocervical canal is marked by short arrows. (Used with permission from Dr. Jodi Dashe.)
Although several investigators have reported excellent results using magnetic resonance (MR) imaging to visualize placental abnormalities, it is unlikely that this technique will replace sonography for routine evaluation anytime soon. That said, MR imaging has proved useful for evaluation of placenta accrete syndromes, discussed on page 445.
Women with placenta previa are managed according to their individual clinical circumstances. The three factors that usually are considered include fetal age and thus maturity, concurrent labor, and bleeding and its severity. Restriction of activity is not necessary unless a previa persists beyond 28 weeks or if clinical findings such as bleeding or contractions develop before this time.
However, antepartum bleeding is common. In one study of 214 women with a previa, 43 percent had an emergent delivery and 46 percent of those were preterm (Eschbach, 2015). But if the fetus is preterm and active bleeding stops, management favors close observation in an obstetric unit. Data are sparse regarding tocolytic administration for uterine contractions. Although quality randomized trials are lacking, most recommend that if tocolytics are given, they be limited to 48 hours of administration (Bose, 2011; Verspyck, 2015). We do not recommend their use.
After bleeding has ceased for approximately 2 days and the fetus is judged to be healthy, the woman can usually be discharged home. However, she and her family must fully appreciate the possibility of recurrent bleeding and be prepared for immediate transport back to the hospital. In some cases, prolonged hospitalization may be ideal. In properly selected patients, no benefits are gained by inpatient compared with outpatient management (Mouer, 1994; Neilson, 2003). In a randomized study by Wing and colleagues (1996a), maternal or fetal morbidity rates did not differ between the two management methods. This trial of inpatient versus home management included 53 women who had a bleeding previa at 24 to 36 weeks’ gestation. Of these women, 60 percent had recurrent bleeding. Also, of all 53 women, half eventually required expeditious cesarean delivery. Home management is more economical, and in one study, hospital stays and costs for maternal-neonatal care were reduced by half with outpatient management (Drost, 1994).
For women who are near term and who are not bleeding, plans are made for scheduled cesarean delivery. Timing is important to maximize fetal growth but to minimize the possibility of antepartum hemorrhage. A National Institutes of Health workshop concluded that women with placenta previa are best served by elective delivery at 36 to 37 completed weeks’ gestation (Spong, 2011). With suspected placenta accrete syndromes, delivery was recommended at 34 to 35 completed weeks. At Parkland Hospital, we prefer to wait until 37 to 38 weeks’ gestation before delivery for placenta previa.
It is axiomatic that with few exceptions, most women with placenta previa will undergo cesarean delivery. Many surgeons recommend a vertical skin incision. Importantly, unscheduled cesarean delivery—many times emergent—becomes necessary in more than half of cases because of hemorrhage, for which about a fourth require blood transfusion (Boyle, 2009; Sabourin, 2012).
Although a low transverse hysterotomy is usually possible, this may cause fetal bleeding if the placental site is anterior. Thus, some prefer a vertical uterine incision. When the placenta is cut through, expeditious delivery is mandatory (Silver, 2015a). That said, even when the incision extends through the placenta, maternal or fetal outcomes are rarely compromised. Of note, rates of anterior placenta previa are approximately equal to rates of posterior previa (Salmanian, 2015; Young, 2013). Anterior previas more often lead to hysterectomy, but posterior previas are equally morbid in all other aspects (Young, 2014).
Following placental removal, uncontrollable hemorrhage may ensue because of the poorly contracted smooth muscle of the lower uterine segment. When hemostasis at the placental implantation site cannot be obtained by pressure, the implantation site can be oversewn with chromic sutures. Cho and associates (1991) described interrupted 0-gauge chromic sutures at 1-cm intervals to form a circle around the bleeding portion of the lower uterine segment. They reported that this controlled hemorrhage in all eight women in whom it was employed. Huissoud and coworkers (2012) also described successful use of circular sutures. Kayem (2011) and Penotti (2012) and their colleagues reported that only 2 of 33 women with placenta previa and no accreta and who were subsequently treated with anterior-to-posterior uterine compression sutures following placenta removal required hysterectomy.
Other methods have been recommended. Kumru and associates (2013) reported success with the Bakri balloon in 22 of 25 cases (Fig. 29-5, p. 473). Diemert and coworkers (2012) described good results with combined use of a Bakri balloon and compression sutures. Albayrak and colleagues (2011) described Foley balloon tamponade. Druzin (1989) proposed tightly packing the lower uterine segment with gauze, and the pack was removed transvaginally 12 hours later. Successful use of hemostatic gel has been reported (Law, 2010; Marinez-Gaytan, 2014). Other methods that are described in Chapter 29 include bilateral uterine or internal iliac artery ligation and pelvic artery embolization (p. 475).
If these more conservative methods fail and bleeding is brisk, then hysterectomy is necessary. Indeed, placenta previa—especially with abnormally adherent placental variations—currently is the most frequent indication for peripartum hysterectomy at Parkland Hospital and other institutions (Hernandez, 2012; Wong, 2011). It is not possible to accurately estimate the effect on hysterectomy rates from previa alone without considering the associated accrete syndromes. It is again emphasized that women with placenta previa implanted anteriorly at the site of a prior uterine incision carry an increased likelihood of associated placenta accrete syndromes and need for hysterectomy.
Of reported rates, in one study of 318 peripartum hysterectomies from in the United Kingdom, 40 percent were done for an abnormally implanted placenta (Knight, 2007). In an Australian study of emergent peripartum hysterectomy, 19 percent were done for placenta previa, and another 55 percent for a morbidly adherent placenta (Awan, 2011). In one audit at Parkland Hospital, 24 percent of 444 women delivered for placenta previa required hysterectomy for hemostasis (Wortman, 2015). In another audit done at Parkland Hospital, 44 percent of all cesarean hysterectomies were done because of bleeding from a placenta previa or accrete syndromes. The technique for peripartum hysterectomy is described in Chapter 26 (p. 423). Special concerns for hysterectomy with accrete syndromes are discussed on page 446.
A marked reduction in maternal mortality rates from placenta previa was achieved during the last half of the 20th century. Still, as shown in Figure 27-9, placental disorders contribute substantively to maternal morbidity and mortality rates. In one review, the maternal mortality ratio was increased threefold to 30 per 100,000 for women with placenta previa (Oyelese, 2006). In a report from the Centers for Disease Control and Prevention, of 3358 maternal deaths in the United States from 2006 to 2010, placenta previa and accrete syndromes accounted for 16 percent of deaths from hemorrhage (Creanga, 2015).
The report from the Consortium on Safe Labor emphasizes the ongoing perinatal morbidity associated with placenta previa (Lai, 2012). Preterm delivery continues to be a major cause of perinatal death (N⊘rgaard, 2012). For the United States in 1997, Salihu and associates (2003) reported a threefold increased neonatal mortality rate with placenta previa that was caused primarily by preterm delivery. Ananth and colleagues (2003b) reported a comparably increased risk of neonatal death even for fetuses delivered at term. This is at least partially related to fetal anomalies that are increased two- to threefold in pregnancy with placenta previa (Crane, 1999).
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