Andrea L. Greiner, MD; Sarah A. Wernimont, MD, PhD; Stephen K. Hunter, MD, PhD 

(Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Iowa Carver College of Medicine)

When was the last time you saw a placenta accreta at the time of repeat cesarean section? Most obstetricians recall one or two adherent placentas over their entire careers. Unfortunately, the increased Cesarean delivery rate of the modern era has made this complication more frequent. Placenta accreta spectrum (PAS) occurs when the placenta abnormally attaches to (or invades into) the myometrium of the uterus. As a result, the placenta does not easily separate from the uterus following delivery of the fetus. The placenta is left in situ and hysterectomy is indicated at time of delivery with significant risk of large volume blood loss, bladder injury, and need for subsequent intensive care1. The purpose of this article is to highlight the growing problem of PAS in Iowa and to outline maternal risk factors, diagnostic techniques and management strategies to optimize maternal and fetal outcomes.  

While the precise mechanisms underlying the development of PAS remain unclear, it is hypothesized that the decidua basalis (thickened endometrium of pregnancy) does not develop normally and cannot prevent the placenta villi from invading into the myometrium2. PAS describes three distinct pathologic findings: placenta accreta, increta and percreta. In placenta accreta, the placenta villi attach to the uterine myometrium while in placenta increta the placenta villi grow into, but not through, the myometrium. Placenta percreta occurs when the placenta grows through the myometrium and uterine serosa, potentially invading the bladder, bowel and adjacent vasculature. It is difficult to distinguish between placenta accreta and increta on diagnostic imaging. Placenta percreta can be diagnosed via obstetric ultrasound and MRI. Placenta percreta can be associated with spontaneous intraabdominal hemorrhage and significant maternal and fetal morbidity.   

In the 1970s, placenta accreta complicated  1 in 4000 pregnancies, increasing to 1 in 2500 in the 1980s and 1 in 500 in the 2000s3. Over these decades, the cesarean delivery rate increased from 10% in the 1970s to 25-30% in the 2000s4. History of prior Cesarean delivery is the most important risk factor for development of PAS. The risk of PAS correlates to the number of prior cesarean sections and presence or absence of placenta previa5. (Table 1) However, any prior uterine surgery including myomectomy, dilation and curettage, endometrial ablation or resection of a uterine septum can also increase risk. Additionally, a history of Asherman syndrome or uterine anomalies is associated with PAS6. Every woman with a history of prior Cesarean delivery and placenta previa (placenta covering cervical os) should undergo ultrasound evaluation for abnormal placentation by a maternal-fetal medicine (MFM) physician.

Obstetric ultrasound is the preferred prenatal diagnostic modality for PAS with a 90% sensitivity and 96% specificity in experienced providers7. Findings on ultrasound include loss of the normal hypoechoic retroplacental zone between the placenta and myometrium underneath the placental bed8. Additional findings include irregular vascular spaces within the placenta giving it a “Swiss cheese” appearance (Figure 1a) ,and myometrial thickness of less than 1 mm under the placenta. Hypervascularity can be noted at the myometrial-placental interface with blood vessels extending beyond the myometrium into the bladder or crossing the serosa of the uterus9. (Figure 1b) MRI has similar sensitivity and specificity to ultrasound and is only indicated in cases where placenta percreta with parametrial invasion is suspected, posterior placenta previa or a morbidly obese patient9,10.

If a pregnant woman has any of the risk factors or imaging findings listed above, a consultation with MFM specialists is recommended for further evaluation. Overall, outcomes are improved when women with suspected PAS are managed by a multidisciplinary team in an experienced center11,12. These women should be cared for in a hospital with the capability to perform cesarean hysterectomy in scheduled or emergent situations as well as a blood bank able to support massive transfusion if needed. At the time of surgery, these women are at significant risk for large volume blood loss, coagulopathy, transfusion of multiple blood products, cesarean hysterectomy, bladder, bowel or vascular injury, cardiac arrest and death. The overall risk of death is up to 6-7% in case series9. The recommendation for delivery timing is 34 weeks for placenta accreta and 32 weeks for placenta percreta with a low threshold to deliver sooner if needed9.

Care for women with MAP at the University of Iowa

In the last few years, the new reality of PAS has changed our practice of obstetrics at the University of Iowa. We are seeing more women with PAS who need to be delivered earlier. As part of a quality improvement initiative, we have collected data since December 2016 on our PAS patients. To date, we have cared for 28 women with PAS who required cesarean hysterectomy. One woman had a pregnancy termination by gravid hysterectomy at 14 weeks with pathology confirmed placenta percreta. The average gestational age at delivery was 29 weeks. Delivery prior to 32 weeks was warranted in 63% (17/27) due to bleeding (vaginal and intraperitoneal). All of the newborns survived to discharge except one who died at 4 months of age due to complications of congenital heart disease. The average blood loss was 2057 ml (range 640-6500) and these women received an average of 2 units of packed red blood cells, (range 1-8 units). These figures for blood loss do not include two maternal deaths due to acute hemorrhage and cardiac arrest after significant antepartum bleeding necessitated emergent delivery at 26 and 34 weeks. Estimated blood loss was 10 liters and 35 liters in these cases and both women received more than 100 units of blood products prior to their deaths. The majority of our cases have had placenta increta or percreta confirmed on pathologic examination of the uterus. (Figure 1c)

We have developed a multi-disciplinary protocol to care for these women directed by University of Iowa MFM faculty physicians. The team includes physicians in gynecologic oncology, general obstetrics, hematology, urology, vascular surgery, radiology, obstetric anesthesia, critical care, blood bank medicine, and neonatology. Additional support is provided by experienced nurses, social workers and hospital spiritual care experts. In the outpatient setting, these women are seen frequently in clinic and in the ultrasound unit. Every effort is made to optimize pre-delivery hemoglobin prior to delivery. Women with MAP are admitted prior to a scheduled procedure at 32-34 weeks gestation for pre-operative preparations or sooner if there is concern for acute clinical decompensation. This is to facilitate safe and rapid delivery if maternal status changes. Upon admission, betamethasone is administered for fetal lung maturity, two sites for IV access are established and blood products are held on the antepartum floor in the event of an acute large volume hemorrhage. At the time of surgery, either planned or emergent, the massive transfusion protocol is activated to guarantee delivery of blood products to the operating room. At the time of cesarean hysterectomy, an obstetrician delivers the infant and gynecologic oncology physicians perform the hysterectomy. The anesthesia team typically includes 2-3 physicians plus a perfusionist to manage the cell salvage machine.

Occasionally, PAS may go undiagnosed prior to a scheduled delivery. (Figure 1d) If an incidental finding of PAS is noted at the time of delivery and the patient and fetus are stable, it is reasonable to close the abdomen, and transfer to a center capable of providing multidisciplinary care if. If delivery must be completed, it is recommended that the placenta remain in situ, hysterotomy closed if the patient is stable. She should then be transferred to a tertiary center where significant blood and surgical support are available. 

The incidence of PAS has increased and providers who care for pregnant women and/or read their ultrasounds must identify women early in pregnancy with risk factors for PAS. These women should be referred to a Maternal-Fetal Medicine specialist to assess their risks and make recommendations if PAS is confirmed. Early identification and referral allows time for discussion with the woman and her family about the issues related to PAS and delivery outlined above. At the University of Iowa, we ideally like to see all women with risk of PAS around 20 weeks gestation to allow adequate counseling, medical optimization and care coordination. Additionally, all obstetric providers need to strive to reduce the rate of primary cesarean sections and consider the option of trial of labor after cesarean section to lower the rate of repeat cesarean sections. Only when these things happen will there be any hope of lowering the incidence of morbidly adherent placenta.

 
Figure 1
 

References

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