Thursday, September 16, 2021

Placenta Accreta Case File

Posted By: Medical Group - 9/16/2021 Post Author : Medical Group Post Date : Thursday, September 16, 2021 Post Time : 9/16/2021
Placenta Accreta Case File
Eugene C. Toy, MD, Edward Yeomans, MD, Linda Fonseca, MD, Joseph M. Ernest, MD

Case 8
A 25-year-old G4P3003 at 19 weeks’ gestation by LMP presents for ultrasound appointment. The fetal anatomic survey is within normal limits but a complete anterior placenta previa is noted. In addition, there is a concern regarding thinning of the myometrium of the lower uterine segment. Color Doppler shows a distance of approximately 1 mm between retroplacental vessels and the uterine serosa-bladder interface. In addition, extensive intraplacental lakes are noted (see Figure 8–1). Given the concern for a placenta accreta, you are contacted by the sonologist performing the ultrasound. You review the patient’s obstetrical and surgical history. Of note, the patient has a history of three prior lower transverse cesarean deliveries. The first one was performed for arrest of active phase after an elective induction of labor at 39 weeks and the next two were performed for a history of cesarean delivery. You have previously discussed with the patient contraception options and the patient has told you that she may want another child but is undecided. You call the patient to discuss the results of her ultrasound.

➤ What is your next step in evaluating the patient?
➤ What are the potential maternal/fetal complications associated with placenta previa/accreta?


ANSWERS TO CASE 8:
Placenta Accreta

Summary: A multipara with multiple prior cesarean deliveries now with ultrasound confirming previa and findings suspicious for placenta accreta.

Next step in evaluating the patient: After confirming the sonographic findings initially found by the sonologist, the next step would be to counsel the patient about placenta accreta and the increased morbidity and mortality it entails. The patient should be assessed for any treatable forms of anemia and also counseled on the possibility of blood transfusion with delivery. Furthermore, preparations should be made to have a planned cesarean delivery if the previa persists with the possibility of a hysterectomy.

Potential maternal/fetal complications associated with placenta previa/accreta: Maternal complications include hemorrhage, infection, risks associated with blood transfusion, increased risk for injury to the bowel, ureters, bladder; hysterectomy/sterilization, intensive care admission, and death. Fetal complications include malpresentation, intrauterine growth restriction (IUGR), and preterm birth.


ANALYSIS
Objectives
  1. Describe the risk factors for placenta previa and accreta.
  2. Describe the clinical presentation of these conditions.
  3. Describe the diagnostic strategy and management of placenta previa and placenta accreta.

Considerations
Classically, placenta previa occurs when placental tissue overlies the internal cervical os; however, it can also occur when placental tissue is located next to or near the internal cervical os. The incidence of placenta previa is gestational age-dependent. It is a common finding before 20 weeks’ gestation, occurring in 1% to 6% of pregnant women during that time period. That said, nearly 90% of these cases demonstrate resolution of the placenta previa by the third trimester. The incidence of placenta previa after the second trimester is approximately 4 per 1000 pregnancies (0.4%). The recurrence rate of placenta previa is 4% to 8%1 (Level III).

Risk factors for placenta previa include prior cesarean delivery, multiparity, advanced maternal age, prior uterine surgery, smoking, and multiple gestations.

This patient has two identifiable risk factors for placenta previa: multiparity and three prior cesarean deliveries. Multiple cesarean deliveries and ultrasound findings of complete previa also increase the risk for placenta accreta, or abnormal invasion of the placenta into the myometrium.

The diagnosis of placenta previa is made using ultrasound, either transvaginal or transabdominal. Transvaginal ultrasound has been shown to be superior to the transabdominal approach in detecting placenta previa. The advantage is that there are fewer false-positive diagnoses while being a safe approach in experienced hands. As with most cases, this patient was diagnosed with a placenta previa on routine ultrasound in the second trimester. In addition, ultrasound findings were suspicious for accreta. Although placenta accreta may not be definitely diagnosed by ultrasound imaging, the sensitivity and specificity of ultrasound is approximately 80% and 95%, respectively.

Management of a patient with a placenta previa and suspected accreta depends on whether or not the patient has active bleeding. This patient was diagnosed at her routine anatomy ultrasound and is without complaints of vaginal bleeding. Serial sonograms are recommended to assess placental location. This patient with a complete previa should be cautioned to seek emergency care if there is any vaginal bleeding. Although there are no data to support the efficacy of avoiding intercourse and excessive activity, it is reasonable to discuss with the patient that these should be avoided. Bedrest at home is not recommended as there is no evidence to support it is of any benefit.

Furthermore, if vaginal bleeding develops, the patient should ideally inform caregivers that she was diagnosed with a placenta previa and possible accreta so that the unbeknownst provider can avoid performing a digital cervical examination. This patient should also be evaluated for anemia periodically during pregnancy so that iron supplementation can be administered in preparation for delivery. The patient should also be counseled regarding the increased risk of antepartum and postpartum hemorrhage, possible blood transfusion, and risk of hysterectomy as a lifesaving procedure. It is important to discuss the patient’s desire for future fertility in advance. She should be counseled that a reasonable effort will be made to preserve her fertility if she desires, as long as it does not comprise her health.


APPROACH TO
Placenta Previa/Accreta

There are four types of placenta previa. First, a complete placenta previa occurs when the placenta completely covers the internal os. Second, a partial placenta previa occurs when the placenta partially covers the internal os. Third, a marginal placenta previa happens when the placenta is located next to internal os. Finally, a low-lying placenta occurs when the placental margin is within 2 cm of the internal os but not next to the internal os.

Although the classic clinical presentation for placenta previa is painless vaginal bleeding, it is important to note that patients with placenta previa may also have painful bleeding due to marginal separation of the abnormally implanted placenta or secondary to contractions. Bleeding from a placenta previa can occur anytime throughout pregnancy; however, it usually does not occur until the late second trimester or beyond. During this time in pregnancy, bleeding may occur due to the formation of the lower uterine segment and dilation of the internal os resulting in tearing of the placental attachments. Moreover, muscle fibers comprising the lower uterine segment may be unable to constrict the bleeding vessels thus further intensifying vaginal bleeding.

Once the diagnosis of placenta previa has been made and in the absence of labor or vaginal bleeding, management would include repeat ultrasound at 32 to 34 weeks for placenta location. With advancing gestational age, the lower segment stretches allowing the placenta to localize away from the internal os. This “migration” occurs most often when the placenta does not completely cover the internal os. Persistence to term can be predicted based on the relationship between the placenta and the internal os in the second trimester. The majority of cases where the tip of the placenta does not touch or cover the internal os resolve2 (Level II).

On the other hand, if there is active vaginal bleeding from a placenta previa, the patient should be stabilized, the fetus monitored, and both should be closely observed to assess for any signs of maternal and/or fetal compromise. Antenatal corticosteroids should be administered if vaginal bleeding occurs between 24 and 34 weeks. Two large-bore intravenous cannulas should be placed and blood should be sent for a blood count and type and screen (or cross) depending on the degree of bleeding. It is important to verify that the blood bank can provide 4 to 6 units of packed red blood cells and coagulation factors if necessary. Rh immunoglobulin should be administered to those who are Rh negative. Assessment for fetal-maternal hemorrhage with either Kleihauer-Betke test or flow cytometry should also be performed to determine if additional Rh immunoglobulin is necessary in these women. The use of tocolytics is controversial. The rationale for their use in those with bleeding and contractions is based on the logic that contractions may cause bleeding which in turn can lead to more contractions and bleeding. The benefit of tocolytic therapy has been demonstrated in two studies where prolongation of pregnancy and higher birth weights were noted; however, the data is limited and the results from these small studies should therefore be interpreted with caution3,4 (Level II). Delivery may be necessary if there is a continued hemorrhage and/or nonreassuring fetal heart rate tracing at any gestational age. A lower threshold for delivery should also be considered for continued bleeding near term. Neonatology consultation to discuss the risks of prematurity is also of benefit to the patient and her family.

If bleeding has stopped and both fetal and maternal status is stable, the patient should be observed for any further bleeding. The decision to observe the patient as an inpatient or as an outpatient is dependent on the initial quantity of bleeding and the risk of recurrent bleeding. Outpatient management
depends on the ability of the patient to return to the hospital in a timely fashion if bleeding recurs, her ability to rest at home and understand the risk of outpatient management, and the ability to call or come to the hospital if she has another bleeding episode. The only randomized trial of inpatient versus outpatient management of 53 women showed no significant difference in maternal or fetal outcomes5 (Level II).

If the placenta previa persists into the third trimester, consideration should be given to timing of delivery. It is preferable to perform a cesarean delivery under controlled conditions rather than in an emergency. As gestational age increases, the risk of bleeding also increases. Testing fetal lung maturity via amniocentesis at 36 to 37 weeks’ gestation is reasonable, although this approach is based primarily on expert opinion. The route of delivery for placenta previa is abdominal. This also includes low lying placentas that are within 2 cm of the internal os. Ideally the uterine incision should be made away from the placenta in order to avoid incising or lacerating fetal-placental vessels; however, even with knowledge of the placental location before delivery this cannot always be avoided. If such is the case, the fetus should be delivered as quickly as possible.

Placenta accreta occurs when there is an abnormally firm attachment of placental villi to the uterine wall with the absence of the normal intervening deciduous basalis and Nitabuch layer. There are three variants of this condition. In the most common form, accreta, the placenta is attached directly to the myometrium. When the placenta extends into the myometrium it is termed placenta increta. Last, when the placenta extends through the entire myometrial layer and uterine serosa it is termed placenta percreta. Over the past two decades, the reported incidence of placenta accreta ranged from 1 in 533 to 1 in 2510 deliveries6,7 (Level II). However, as the national rate of cesarean deliveries continues to increase over time, the incidence of placenta accreta will likewise increase as well.

Several risk factors for placenta accreta have been identified. The two most important appear to be prior cesarean delivery and placenta previa. In women with placenta previa the incidence of placenta accreta appears to correlate with the number of previous cesarean sections. Clark et al reported a 5% incidence of placenta accreta among women with placenta previa and no previous cesarean sections8 (Level II). The incidence increased to 24% with one previous cesarean section and to 45% with two or more. Among 723 women with prior cesarean delivery and previa, Silver et al reported the risk for accreta to be 3%, 11%, 40%, 61%, and 67% for one, two, three, four, and five or more cesarean deliveries, respectively. Among 29,409 women with cesarean delivery and no previa the risk for accreta was 0.03%, 0.2%, 0.1%, 0.8%, 0.8%, 4.7% for one, two, three, four, five, and six or more cesarean deliveries, respectively9 (Level II). Advanced maternal age and placental location with respect to the previous uterine scar have also been reported to be independent risk factors for placenta accreta among women with placenta previa.

Miller reported a 2.1% incidence of accreta in women with placenta previa who were less than 35 years of age and had no previous cesareans. The incidence increased to 38.1% in women who were 35 years of age or older with two or more previous cesarean sections and a placenta previa overlying the uterine scar6 (Level II).

Placenta accreta should be suspected in all women with placenta previa. A definitive diagnosis of accreta is not possible prior to delivery. That said, ultrasonography has yielded encouraging results in the prospective diagnosis of placenta accreta. The use of ultrasonography and color Doppler findings (diffuse intraparenchymal placental lacunar flow, bladder-uterine serosa hypervascularity, prominent subplacental venous complex, loss of subplacental Doppler vascular signals) has yielded sensitivities of approximately 80% and specificities of approximately 95% for the detection of accrete10,11 (Level II). Using ultrasound color flow mapping, Twickler found if the myometrial thickness under the placenta was less than 1 mm, this was predictive of myometrial invasion with a sensitivity of 100%, specificity 72%, positive predictive value (PPV) 72%, and negative predictive value (NPV) 100% (Figure 8–1)12 (Level II).MRI has been described to diagnose placenta accreta, although the sensitivity does not appear to be superior to sonography. Warshak et al evaluated the accuracy of


Ultrasound of a placenta accreta

Figure 8–1. Ultrasound of a placenta accreta (increta). Note the hypervascularity
at the bladder-lower segment interface as well as the inability to define a layer of
myometrium between the placenta and the bladder. There is also lacunar lakes
noted in the placenta.(Courtesy of Dr. Richard H. Lee)


sonography and MRI in the antenatal diagnosis of placenta accreta. Of 39 cases of confirmed placenta accreta, sonography had a sensitivity of 77% and specificity of 96% whereas gadolinium-enhanced MRI had a sensitivity of 88% and specificity of 100% and was able to exclude placenta accreta in 14/14 cases. The use of MRI must take into account cost, accessibility, and if gadolinium is used, the risks and benefits of fetal exposure to contrast agents13 (Level II).

In women with placenta previa who are considered to be at high risk for placenta accreta, cesarean delivery should be performed electively. The timing of delivery differs among institutions. Delivery timing is based on several factors including patient stability, risk of future bleeding, and fetal maturity. That said, most experts generally agree that delivery should occur at approximately 35 to 37 weeks’ gestation. The patient should be counseled preoperatively regarding the risks of hemorrhage, transfusion, and hysterectomy. The operating room should be staffed by experienced personnel, equipped with appropriate hysterectomy instruments, and blood products/blood salvage equipment should be available. The use of prophylactic intravascular balloon catheters for placenta accreta have failed to produce any substantial decrease in maternal morbidity14 (Level II). Preoperative ureteral stents may be placed to avoid ureteral injury. It is important that other surgical specialties be available including gynecologic oncology and urology services.

At cesarean delivery the uterine incision is made vertically away from the suspected placental location. The fetus is delivered, spontaneous delivery of the placenta is awaited, or gentle traction is applied on the cord to await delivery of placenta. Attempts to manually deliver the placenta can cause massive hemorrhage if there is indeed a placenta accreta. However, it is important for the physician to be aware that focal placenta accreta may occur which may be treated with conservative approaches. If placental delivery is unsuccessful or if uncontrollable hemorrhage ensues, the surgeon should leave the placenta in place and proceed with hysterectomy. Hysterectomy remains the procedure of choice (Figures 8–2 and 8–3).

Control of potentially life-threatening hemorrhage is the first priority; however, the patient’s desire for future fertility must be taken into consideration. If the patient is hemodynamically stable and strongly desires future fertility, conservative management may be cautiously considered—keeping in mind the literature regarding conservative management is based on case series or reports. The risks of conservative management include delayed hemorrhage (requiring reoperation) and infection. If the patient is unstable, conservative management is not an option.

Conservative techniques that have been described include curettage and/or over-sewing the placental bed, or wedge resection of the area of accreta with subsequent repair of the myometrium. In the vast majority of cases these techniques have been applied in the setting when a focal accreta is encountered after attempted removal of the placenta. Planned conservative management has been described in case reports when a placenta accreta is diagnosed before delivery and the patient strongly desires future fertility, this


cesarean hysterectomy specimen

Figure 8–2. The cesarean hysterectomy specimen. Note the placenta can be visualized
underneath the uterine serosa.(Courtesy of Dr. Richard H. Lee)


involves leaving the placenta in situ thereafter adjunctive therapy is administered either with uterine artery embolization, methotrexate, or delayed removal. These methods of management have not been subject to randomized control trials and should be considered investigational. This approach should only be considered in patients who strongly desire future fertility and who understand and accept the risks of delayed hemorrhage, infection, and death. The patient should be counseled that this approach cannot be used if she has profuse bleeding or is hemodynamically unstable. Timmermans et al. reviewed 60 pregnancies managed with the conservative management. The most common complication was that of vaginal bleeding (21/60). The timing of blood loss ranged from immediately postpartum up to 3 months after delivery. Treatment failure due to vaginal bleeding occurred in 15% of case (9/60). Fever occurred in 21/60 cases, 11/60 had endomyometritis, and 2/60 required hysterectomy for definitive treatment. Importantly, the authors caution that the number of complications may be falsely lowered due to publication bias of reported successful cases15 (Level II).


macroscopic cross section of the specimen

Figure 8–3. A macroscopic cross section of the specimen. Note the invasion of the
placenta into the myometrium. The final pathologic diagnosis was placenta increta.
(Courtesy of Dr. Richard H. Lee)


Clinical Pearls

See US Preventive Services Task Force Study Quality levels of evidence in Case 1
➤ Placenta previa is a common diagnosis before 20 weeks’gestation (1%-6%) (Level II-2).
➤ Approximately 90% of cases of placenta previa diagnosed before 20 weeks’ resolve (Level II-2).
➤ The recurrence risk of placenta previa is 4% to 6% (Level II-3).
➤ Placenta accreta should be suspected in any patient with a prior cesarean delivery and a placenta previa (Level II-2).
➤ In an unstable, bleeding patient with a suspected placenta accreta, cesarean hysterectomy is the procedure of choice.


CONTROVERSIES
  • The gestational age at which to electively deliver placenta previa.
  • The gestational age at which to electively deliver a suspected placenta accreta.
  • If MRI is of any added benefit to ultrasound in making the diagnosis of placenta accreta.
REFERENCES

1. Oyelese Y, Smulian JC. Placenta previa, placenta accreta, and vasa previa. Obstet Gynecol. 2006 Apr;107(4):927-941. The authors perform an in-depth review on the management of placenta previa, accreta, and vasa previa (Level III). 

2. Taipale P, Hiilesmaa V, Ylostalo P. Transvaginal ultrasonography at 18-23 weeks in predicting placenta previa at delivery. Ultrasound Obstet Gynecol. 1998 Dec;12(6):422-425. The authors assess the persistence of placenta previa at the time of delivery (Level II). 

3. Besinger RE, Moniak CW, Paskiewicz LS, Fisher SG, Tomich PG. The effect of tocolytic use in the management of symptomatic placenta previa. Am J Obstet Gynecol. 1995 Jun;172(6):1770-1775; discussion 5-8. The authors studied 112 preterm pregnancies with placenta previa and initial bleeding. They assessed outcomes after the administration of magnesium sulfate and/or betasympathomimetics. They found tocolytic therapy may prolong pregnancy and increase birthweight, but does not appear to alter the frequency or severity of bleeding (Level II). 

4. Sharma A, Suri V, Gupta I. Tocolytic therapy in conservative management of symptomatic placenta previa. Int J Gynaecol Obstet. 2004 Feb;84(2):109-113. The authors found the use of ritodrine may prolong pregnancies and increase the birthweight in patients with symptomatic placenta previa (Level II). 

5. Wing DA, Paul RH, Millar LK. Management of the symptomatic placenta previa: a randomized, controlled trial of inpatient versus outpatient expectant management. Am J Obstet Gynecol. 1996 Oct;175(4 Pt 1):806-811. The authors found that outpatient management may be used in a selected group of patients with symptomatic placenta previa (Level II). 

6. Miller DA, Chollet JA, Goodwin TM. Clinical risk factors for placenta previaplacenta accreta. Am J Obstet Gynecol. 1997 Jul;177(1):210-214. The authors found among 155,670 delivieries, 1 in 2510 were complicated by a histologically confirmed placenta accreta. They found advanced maternal age and prior cesarean delivery to be independent risk factors for placenta accreta in women with placenta previa (Level II). 

7. Wu S, Kocherginsky M, Hibbard JU. Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol. 2005 May;192(5):1458-1461. An evalution on the incidence of placenta accreta between 1982 and 2002. The incidence of placenta accreta was found to be 1 in 533 (Level II). 

8. Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985 Jul;66(1):89-92. This retrospective cohort study evaluated 97,799 patients and found the risk of placenta previa in an unscarred uterus was 0.26%. The risk of plcenta accreta in the presence of placenta previa in an unscarred uterus was 5%. The risk of placenta previa/accreta was found to be increased with the number of prior cesarean births (Level II). 

9. Silver RM, Landon MB, Rouse DJ, et al. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol. 2006 Jun;107(6):1226-1232. The authors found increased morbidity as well as increased risk for accreta with increasing number of cesarean deliveries (Level II). 

10. Chou MM, Ho ES, Lee YH. Prenatal diagnosis of placenta previa accreta by transabdominal color Doppler ultrasound. Ultrasound Obstet Gynecol. 2000 Jan;15(1):28-35. The authors evaluated the sensitivity (82.4%) and specificity (96.8%) of various color Doppler parameters to diagnose placenta previa/accreta during pregnancy (Level II). 

11. Comstock CH, Love JJ, Jr., Bronsteen RA, et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol. 2004 Apr;190(4):1135-1140. The authors conclude the ultrasonographic appearance of vascular spaces within the placenta (lacunae) has the highest positive predictive value for placenta accreta (Level II). 

12. Twickler DM, Lucas MJ, Balis AB, et al. Color flow mapping for myometrial invasion in women with a prior cesarean delivery. J Matern Fetal Med. 2000 Nov-Dec;9(6):330-335. The authors found that a measurement of < 1 mm for the smallest myometrial thickness or presence of large intraplacental lakes was predictive of myometrial invasion with 100% sensitivity and 72% specficity (Level II). 

13. Warshak CR, Eskander R, Hull AD, et al. Accuracy of ultrasonography and magnetic resonance imaging in the diagnosis of placenta accreta. Obstet Gynecol. 2006 Sep;108(3 Pt 1):573-581. The authors of this cohort study concluded that the combination of ultrasound and MRI would optimize diagnostic accuracy for placenta accreta (Level II). 

14. Shrivastava V, Nageotte M, Major C, Haydon M, Wing D. Case-control comparison of cesarean hysterectomy with and without prophylactic placement of intravascular balloon catheters for placenta accreta. Am J Obstet Gynecol. 2007 Oct;197(4):402 e1-5. This case-control study did not find any significant difference with prophylactic placement of intravascular balloon catheters in patients undergoing cesarean hysterectomy for placenta accreta (Level II). 

15. Timmermans S, van Hof AC, Duvekot JJ. Conservative management of abnormally invasive placentation. Obstet Gynecol Surv. 2007 Aug;62(8):529-539. A review of published literature between 1985 and 2006 that involved conservative management of abnormally invasive placentation (Level II).

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