This bleeding may stimulate further uterine contractions, which, in turn, stimulates further placental separation and bleeding. Rarely are these initial bleeds a major problem, although they may be a reason for hospitalization. In labor, as the cervix dilates and effaces, there is usually placental separation and unavoidable bleeding.
Clinical Importance Morbidities associated with placenta previa include antepartum bleeding relative risk [RR] 9. Placenta previa is also associated with an increase in preterm birth and perinatal mortality and morbidity. Diagnostic Approach The classic clinical presentation of placenta previa is painless bleeding in the late second trimester or early third trimester. However, some patients with placenta previa will experience painful bleeding, possibly the consequence of uterine contractions or placental separation, whereas others will experience no bleeding at all before labor.
Placenta previa may also lead to an unstable lie or malpresentation in late pregnancy. The majority of cases of placenta previa are. Incidence and Risk Factors Placenta previa complicates approximately 0. Although transabdominal sonography is frequently used for placental location, this technique lacks some precision in diagnosing placenta previa.
The superiority of transvaginal sonography over transabdominal sonography can be attributed to several factors: 1.
The transabdominal approach requires bladder filling, which results in approximation of the anterior and posterior walls of the lower uterine segment, with the result that a normally situated placenta may falsely appear to be a previa. Vaginal probes are closer to the region of interest, and typically of higher frequency, and therefore obtain higher resolution images than transabdominal probes. The internal cervical os and the lower placental edge frequently cannot be imaged adequately by the transabdominal approach.
The position of the internal os is assumed rather than actually seen. The fetal head may obscure views of the lower placental edge when using the transabdominal approach, and a posterior placenta previa may not be adequately imaged.
The improved accuracy of transvaginal sonography over transabdominal sonography means that fewer false-positive diagnoses are made; thus, the rate of placenta previa is significantly lower when using transvaginal sonography than when using transabdominal sonography. Translabial sonography has been suggested as an alternative to transvaginal sonography and has been shown to be superior to transabdominal sonography for placental location.
Several studies have demonstrated that the majority of placentas that are in the lower uterine segment in the second trimester will no longer be in the region of the cervix by the time of delivery Table 1.
However, the presence of a low-lying placenta in the second trimester is a risk factor for developing a vasa previa, and therefore, in these cases, a sonogram should be performed later in pregnancy to exclude that condition. Management In the past, suspected placenta previa was managed by vaginal examination and immediate cesarean delivery if placenta previa was confirmed.
It was believed that the first bleed usually occurring in the early third trimester would lead to maternal death.
However, MacAfee23 showed that, in the absence of interference, this almost never happened, and that the high perinatal mortality from placenta previa was primarily due to prematurity, which could be reduced considerably by conservative expectant management and delivery as close to term as possible.
Types of placenta previa. Illustration: John Yanson. Placenta Previa, Accreta, and Vasa Previa. Obstet Gynecol Women who present with bleeding in the second half of pregnancy should have a sonographic examination preferably by the transvaginal approach for placental location prior to any attempt to perform a digital examination. Digital vaginal examination with a placenta previa may provoke catastrophic hemorrhage and should not be performed.
It is reasonable to hospitalize women with placenta previa while they are having an acute bleeding episode or uterine contractions. One to two wide-bore intravenous cannulas should be inserted and blood taken for a full blood count and type and screen. In the absence of massive bleeding or other complications, coagulation studies are not helpful. The blood bank must be capable of making available at least 4. Rh immune globulin should be administered to Rh-negative women.
A Kleihauer-Bettke test for quantification of fetal-maternal transfusion should also be performed in Rhnegative women because the mother may require increased doses of Rh immune globulin. Small studies have suggested a benefit of tocolytic therapy for women with placenta previa who are having contractions. Transvaginal sonogram of a complete placenta previa PP. Note that both the placenta and the internal cervical os arrow are clearly depicted.
A, anterior lip of cervix; P, posterior lip of cervix. The placenta just overlaps the internal os. One can see how this could become a partial placenta previa covering just the anterior lip of the cervix if cervical dilation were to occur. Diagram demonstrating the technique for transvaginal sonography of placenta previa. T, transvaginal transducer; A, anterior lip of cervix; P, posterior lip of cervix.
Complete placenta previa is shown completely covering the internal os arrow. The transvaginal transducer lies within the vagina, about 2 cm from the anterior lip of the cervix. The angle between the transducer and the cervical canal is 35 degrees, demonstrating why the probe does not enter the cervix.
Table 1. Sharma and colleagues24 carried out a small randomized study using the -adrenergic ritodrine and found a significant prolongation in pregnancy and higher birth weights in women treated with ritodrine when compared with women treated with placebo.
Thus, cautious use of tocolytics in women with placenta previa who are having contractions, when both mother and fetus are stable, appears reasonable. Steroids should be administered in women between 24 and 34 weeks of gestation, generally at the time of admission for bleeding, to promote fetal lung maturation.
The patient and her family should have a neonatology consultation so that the management of the infant after birth may be discussed. In women who have a history of cesarean delivery or uterine surgery, detailed sonography should be performed to exclude placenta accreta.
Because prematurity is the main cause of perinatal mortality associated with placenta previa, it is desirable to prolong gestation as long as safely possible. Therefore, before 32 weeks of gestation, moderate-to-severe bleeding when there is no maternal or fetal compromise may be managed aggressively with blood transfusions, rather than resorting to delivery.
Specifically, the patient should have access to a telephone, have a responsible adult and transportation available at all times, and must live within reasonable distance of a hospital. She should return to the hospital imme-. Although there are no data to support the efficacy of avoidance of intercourse and excessive activity, common sense suggests that these should be avoided.
Similarly, bedrest is often advised, but there is no evidence that demonstrates that this practice is beneficial. Outpatient Versus Inpatient Management Whether women with placenta previa should be managed as inpatients or outpatients has been a matter of controversy. A few retrospective studies have addressed this issue and have found no difference in outcomes, whether patients were managed in hospital or at home, and found that outpatient management may be associated with lower costs.
However, in another retrospective study, DAngelo and Irwin29 found an increase in perinatal mortality, lower gestational age at delivery, increased neonatal hospitalization duration, and neonatal morbidity among women who were managed as outpatients when compared with those managed expectantly as inpatients.
In one of the few prospective randomized studies dealing with placenta previa, Wing et al30 randomized 53 women with placenta previa at gestational ages between 24 and 36 weeks, who had been initially stabilized in hospital, to inpatient or outpatient management and found no significant difference in outcomes.
Thus, women who are stable and asymptomatic, and who are reliable and have quick access to hospital, may be considered for outpatient management. Cerclage Arias31 randomized 25 women who were admitted to hospital with symptomatic placenta previa at 24 30 weeks gestation to cerclage or no cerclage and found a higher mean birth weight and gestational age at delivery and fewer neonatal complications in the cerclage group.
Women with cerclage had lower hospitalization costs and fewer bleeding episodes. However, in a later study, Cobo and colleagues32 randomized 39 women with placenta previa at 24 30 weeks to cerclage or no cerclage and found no statistically significant differences in gestational age at delivery, prolongation of pregnancy, or in amount of blood lost between the 2 groups.
In view of the lack of convincing data to support cerclage in these women, cerclage should not be performed for treatment of placenta previa. Mode of Delivery There is consensus that a placenta previa that totally or partially overlies the internal cervical os requires delivery by cesarean. However, the mode of delivery when the placenta lies in proximity to the internal os is more controversial. Three small retrospective studies using transvaginal or translabial sonography have evaluated the role of ultrasonography in determining the optimal mode of delivery for women whose placentas were in proximity to the internal cervical os.
Conversely, among women with a placenta-internal os distance less than 2 cm, the overwhelming majority required cesarean delivery, usually for bleeding. However, in none of these studies were the clinicians blinded to the results of the scan, and this may have influenced obstetric management.
Furthermore, these studies had relatively small numbers. Nonetheless, the studies suggest that women with placenta previa should have a transvaginal sonogram in the late third trimester, and that those with a placental edge to internal os distance of less than 2 cm should be delivered by cesarean. It has been our experience that women with a placentainternal os distance of less than 2 cm who undergo a trial of labor almost invariably experience significant bleeding during labor, necessitating cesarean delivery.
Consequently, it is now our practice to deliver these women by elective cesarean. Women whose placentas are 2 cm or more from the os undergo a normal labor. It is important though to realize that, in women with a placenta that extends into the noncontractile lower uterine segment who have a vaginal delivery, there is potential for postpartum hemorrhage.
When there is an anterior placenta previa, there is a considerable likelihood of incising through the placenta during delivery.
This could lead to significant maternal and fetal blood loss and also to difficulty with delivery, but this rarely constitutes a significant problem. Alternative strategies have been proposed and used to avoid incision into the placenta. These include use of a fundal vertical uterine incision, especially in women who have no desire for further childbearing.
Sonography before surgery for placental location enables the surgeon to plan the most appropriate incision. The infant is delivered as rapidly as possible, and the cord is clamped immediately to avoid hemorrhage from fetal vessels. Timing of Delivery As gestational age advances, there is an increased risk of significant bleeding, necessitating delivery. It is preferable to perform a cesarean delivery for placenta previa under controlled scheduled conditions rather than as an emergency.
Therefore, in a stable patient, it is reasonable to perform a cesarean delivery at 36 37 weeks of gestation, after documentation of fetal lung maturity by amniocentesis. If the amniocentesis does not demonstrate lung maturity, we deliver the women by elective cesarean at 38 weeks, without repeating the amniocentesis, if they remain stable, or earlier if bleeding occurs or the patient goes into labor.
Anesthesia for Delivery In the past, it was generally recommended that cesarean deliveries for placenta previa be performed under general anesthetic. At least 2 studies, including a prospective randomized trial, have found that cesarean deliveries for placenta previa performed under general anesthetic were associated with significantly greater estimated blood loss and greater requirements for blood transfusion than those performed under regional anesthesia,38,39 possibly due to increased uterine relaxation associated with general anesthetic.
Otherwise, there was no difference in the incidence of intraoperative or anesthesia complications between regional and general anesthesia. A survey of anesthesiologists in the United Kingdom found a wide variety of opinions regarding whether general or regional anesthesia should be used for cesarean for placenta previa.
However, anesthesiologists who did more obstetric anesthesia were more likely to employ regional anesthesia. When the placenta invades the myometrium, the term placenta increta is used, whereas placenta percreta refers to a placenta that has invaded through the myometrium and serosa, sometimes into adjacent organs, such as the bladder.
The term placenta accreta is often used interchangeably as a general term to describe all of these conditions. Incidence and Risk Factors Miller and colleagues,45 reviewing , deliveries at their hospital between and , found that 62 one in 2, were complicated by placenta accreta.
The incidence of placenta accreta is increasing, primarily as a consequence of rising cesarean delivery rates. A recent study by Wu and colleagues46 looking at placenta accreta over a year period found an incidence of 1 in pregnancies at their institution. Placenta accreta occurs most frequently in women with one or more prior cesarean deliveries who have a placenta previa in the current pregnancy. It has been proposed that the abnormality of the placental-uterine interface in women with placenta accreta will lead to leakage of fetal alpha-fetoprotein into the maternal circulation, resulting in elevated levels of maternal serum alpha-fetoprotein MSAFP.
Although these studies are small, they suggest that women with elevated MSAFP levels with no other obvious cause should be considered at increased risk of placenta accreta. Clinical Significance Placenta accreta may lead to massive obstetric hemorrhage, resulting in such complications as disseminated intravascular coagulopathy, need for hysterectomy, surgical injury to the ureters, bladder, and other viscera, adult respiratory distress syndrome, renal failure, and even death.
Pathophysiology Placenta accreta is thought to be due to an absence or deficiency of Nitabuchs layer or the spongiosus layer of the decidua. Histology usually shows that the trophoblast has invaded the myometrium without intervening decidua. Hysterectomy specimen demonstrating placenta accreta.
This placenta accreta was diagnosed prenatally. The placenta p has invaded the myometrium arrow and after hysterectomy could not be separated from the uterus.
There were no planes of demarcation between placenta and myometrium. Grayscale sonogram of placenta percreta. Note the prominent placental lacunae arrows giving the lower uterine segment a moth-eaten appearance.
The diagnosis was confirmed at delivery. Diagnostic Approach It is important to make the diagnosis of placenta accreta prenatally because this allows effective management planning to minimize morbidity. This diagnosis is usually made by ultrasonography or magnetic resonance imaging MRI. Placenta accreta should be suspected in women who have both a placenta previa and a history of cesarean delivery or other uterine surgery.
These lacunae may give the placenta a moth-eaten or Swiss cheese appearance Fig. The risk of placenta accreta increases with an increased number of lacunae. Thus, in the majority of clinical situations, Doppler should not be the primary technique used to diagnose placenta accreta. A retrospective review of images of first-trimester sonograms of cases of placenta accreta found that, in all the cases, the gestational sac was in the lower uterine segment and that the gestational sac was abnormally close to the uterine scar, suggesting attachment to the scar.
Therefore, at the present time, sonography is the primary imaging modality for diagnosing accreta. However, when there is a posterior placenta accreta, ultrasonography may be less than adequate, and MRI. Ultrasonography Several studies have documented the efficacy of sonography in the diagnosis of placenta accreta. These include irregularly shaped placental lacunae vascular spaces within the placenta, thinning of the myometrium overlying the placenta, loss of the retroplacental clear space, protrusion of the placenta into the bladder, increased vascularity of the uterine serosabladder interface, and, on Doppler ultrasonography, turbulent blood flow through the lacunae Figs.
Therapeutic Approach It is generally accepted that placenta accreta is ideally treated by total abdominal hysterectomy. In addition, there is almost universal consensus that the placenta should be left in place; attempts to detach the placenta frequently result in massive hemorrhage. However, the physician should be aware that focal placenta accreta may exist that may not require such aggressive therapy.
It is better to perform surgery for placenta accreta under elective, controlled conditions rather than as an emergency without adequate preparation. Therefore, scheduled delivery at 36 37 weeks of gestation, after documentation of fetal lung maturity by amniocentesis, seems reasonable.
If amniocentesis fails to document fetal lung maturity, the patient, if stable, should be delivered by cesarean by 38 weeks, or earlier, if she bleeds or goes into labor. A study comparing emergency with elective peripartum hysterectomy found that women in the emergency hysterectomy group had greater intraoperative blood loss, were more likely to have intraoperative hypotension, and were more likely to receive blood transfusions than women who had elective obstetric hysterectomies.
The patient should be counseled preoperatively about the need for hysterectomy and the likely requirement for transfusion of blood and blood products. It is important that delivery be performed by an experienced obstetric surgeon, with other surgical specialties such as urology and gynecological oncology readily available if required.
It is not unusual for the lower uterine segment to be markedly enlarged and vascular, with distortion of normal anatomy and tissue planes. Preoperative cystoscopy with placement of ureteric stents may help prevent urinary tract injury. At our center, we usually insert a 3-way Foley catheter in the bladder via the urethra, allowing simultaneous irrigation and drainage of the bladder during the surgery.
In instances where tissue plane identification is difficult because of adhesions or the invasive placenta, we have the option of distending the bladder to aid in its identification and then emptying it to avoid injury while we proceed with surgery. Use of a vertical skin incision facilitates adequate exposure. Generally, a vertical incision in. There should be no attempt to detach the placenta from the uterine wall. The edges of the uterine incision should be oversewn for hemostasis, after which a total abdominal hysterectomy should be performed.
Although some have advocated supracervical hysterectomy, in the majority of cases the lower uterine segment is involved in the morbid adhesion and therefore needs to be removed. It is important to minimize blood loss and ensure that the blood lost is replaced promptly and adequately. Thus, coagulation factors should be replaced liberally, adequately, and quickly. Donor-directed blood transfusions and use of a blood cell saver may reduce the need for transfusion with blood from another donor.
Balloon Catheter Occlusion and Embolization Balloon catheter occlusion or embolization of the pelvic vessels decreases blood flow to the uterus and potentially leads to reduced blood loss and makes it possible to perform surgery under easier, more controlled circumstances, with less profuse hemorrhage. In one approach, several investigators preoperatively place occlusive balloon catheters in the internal iliac arteries.
These catheters are inflated after delivery of the fetus, allowing surgery under controlled circumstances, and are deflated after the surgery. In the other major approach, catheters with or without balloons are placed preoperatively in the internal iliac arteries, and embolization of the vessels is performed after delivery of the fetus and before hysterectomy. These studies are for the most part retrospective and limited by small numbers. Levine and colleagues62 did not find that pelvic vessel embolization improved surgical outcomes when compared with women who did not have embolization.
Kidney et al61 reported 5 cases of placenta accreta where prophylactic hypogastric artery balloon catheter embolization was performed after the cesarean delivery and before hysterectomy.
These authors suggested. A study by Alvarez and colleagues60 found that elective embolization resulted in improved outcomes when compared with embolizations done emergently. Affiliations 1 Nassau University Medical Center. Continuing Education Activity Placenta previa is the complete or partial covering of the internal os of the cervix with the placenta. Introduction Placenta previa is the complete or partial covering of the internal os of the cervix with the placenta.
Etiology The underlying cause of placenta previa is unknown. Epidemiology Placenta previa affects 0. Pathophysiology Placenta previa is the complete or partial covering of the cervix. History and Physical The risks factors for placenta previa include a history of advanced maternal age age greater than 35 years old , multiparity, smoking, history of curettage, use of cocaine, and history of cesarean section s. Evaluation Routine sonography in the first and second trimester of pregnancy provides early identification of placenta previa.
Delivery A cesarean section should optimally occur under controlled conditions. Differential Diagnosis Vaginal bleeding during pregnancy can be due to numerous factors. Prognosis Neonatal Prognosis There is a threefold to fourfold increased neonatal mortality and morbidity rate with placenta previa primarily from preterm delivery. Complications Vaginal bleeding secondary to placenta previa can lead to postpartum hemorrhage requiring a blood transfusion, hysterectomy, maternal intensive care admission, septicemia, and maternal death.
Deterrence and Patient Education Placenta previa is the covering of the internal cervical os preventing a safe vaginal delivery. Delivery should be performed from 36 to 37 full weeks, via cesarean section, in uncomplicated cases. Bed rest, avoiding intercourse, and avoiding digital examinations are recommended.
Any manipulation of the placenta can lead to hemorrhage. Patients with placenta previa should go to the emergency room if they have any episodes of vaginal bleeding. Prior history of placenta previa and a history of cesarean sections may increase a patient's risk for placenta accreta.
If there is a concern for placenta accreta, increta, or percreta, then a cesarean hysterectomy may need to be performed. Enhancing Healthcare Team Outcomes Placenta previa can lead to serious consequences and requires immediate attention to the presentation of vaginal bleeding.
Review Questions Access free multiple choice questions on this topic. Comment on this article. References 1. Anterior placenta previa in the mid-trimester of pregnancy as a risk factor for neonatal respiratory distress syndrome. PLoS One. Prophylactic uterine artery embolization in second-trimester pregnancy termination with complete placenta previa.
J Int Med Res. Advanced maternal age and its association with placenta praevia and placental abruption: a meta-analysis. Cad Saude Publica. Bleeding control using intrauterine continuous running suture during cesarean section in pregnant women with placenta previa.
Arch Gynecol Obstet. Placenta Accreta Spectrum. N Engl J Med. Silver RM. Obstet Gynecol. Effect of site of placentation on pregnancy outcomes in patients with placenta previa. Findeklee S, Costa SD. Geburtshilfe Frauenheilkd. Curr Med Sci. Relationship between placenta location and resolution of second trimester placenta previa. Carusi DA. Clin Obstet Gynecol. Association between tobacco use in pregnancy and placenta-associated syndromes: a population-based study. Pedigo R. First trimester pregnancy emergencies: recognition and management.
Emerg Med Pract. Management of the symptomatic placenta previa: a randomized, controlled trial of inpatient versus outpatient expectant management. Am J Obstet Gynecol. Riveros-Perez E, Wood C. Retrospective analysis of obstetric and anesthetic management of patients with placenta accreta spectrum disorders.
Int J Gynaecol Obstet. Anesth Analg. Prophylactic abdominal aortic balloon occlusion: An effective method of controlling hemorrhage in patients with placenta previa or accreta. Exp Ther Med. Case Rep Obstet Gynecol. Vaginal delivery in women with a low-lying placenta: a systematic review and meta-analysis. Matsuzaki S, Kimura T. Vasa Previa. If the mother experiences bleeding that cannot be controlled, immediate cesarean delivery is usually done regardless of the length of the pregnancy.
Some marginal previas can be delivered vaginally, although complete or partial previas would require a cesarean delivery. Most physicians will also recommend limiting the following activities:. With all the excitement and anticipation of a healthy delivery, receiving the diagnosis of placenta previa can be a very shocking and frustrating experience.
There are support groups for bed rest mothers and even some for mothers with placenta previa. They are available to help you through this difficult time. Your doctor, midwife , or doula should be able to assist you in finding support groups or other women who have also had placenta previa.
Scott, James R. Placenta Previa. How Common Is Placenta Previa? It is more common in women who have had one or more of the following: More than one child A cesarean birth Surgery on the uterus Twins or triplets What Are The Different Types?
Complete Previa: the cervical opening is completely covered Partial Previa: a portion of the cervix is covered by the placenta Marginal Previa: extends just to the edge of the cervix What Are The Symptoms? Other Signs and Symptoms Include: Premature contractions Baby is breech, or in a transverse position Uterus measures larger than it should according to gestational age What Is The Treatment? Most physicians will also recommend limiting the following activities: Avoid intercourse Limit traveling Avoid pelvic exams What Causes Placenta Previa?
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