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
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 specialistto 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
- Silver, R. M. & Branch, D. W. Placenta Accreta Spectrum. N Engl J Med 378, 1529-1536, doi:10.1056/NEJMcp1709324 (2018).
- Jauniaux, E. & Jurkovic, D. Placenta accreta: pathogenesis of a 20th century iatrogenic uterine disease. Placenta 33, 244-251, doi:10.1016/j.placenta.2011.11.010 (2012).
- Wu, S., Kocherginsky, M. & Hibbard, J. U. Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol 192, 1458-1461, doi:10.1016/j.ajog.2004.12.074 (2005).
- MacDorman, M. F., Menacker, F. & Declercq, E. Cesarean birth in the United States: epidemiology, trends, and outcomes. Clin Perinatol 35, 293-307, v, doi:10.1016/j.clp.2008.03.007 (2008).
- Silver, R. M. et al. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol 107, 1226-1232, doi:10.1097/01.AOG.0000219750.79480.84 (2006).
- Baldwin, H. J. et al. Antecedents of Abnormally Invasive Placenta in Primiparous Women: Risk Associated With Gynecologic Procedures. Obstet Gynecol 131, 227-233, doi:10.1097/AOG.0000000000002434 (2018).
- D'Antonio, F., Iacovella, C. & Bhide, A. Prenatal identification of invasive placentation using ultrasound: systematic review and meta-analysis. Ultrasound Obstet Gynecol 42, 509-517, doi:10.1002/uog.13194 (2013).
- Jauniaux, E. et al. FIGO consensus guidelines on placenta accreta spectrum disorders: Prenatal diagnosis and screening. Int J Gynaecol Obstet 140, 274-280, doi:10.1002/ijgo.12408 (2018).
- Publications Committee, S. f. M.-F. M. & Belfort, M. A. Placenta accreta. Am J Obstet Gynecol 203, 430-439, doi:10.1016/j.ajog.2010.09.013 (2010).
- Jauniaux, E., Collins, S. & Burton, G. J. Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging. Am J Obstet Gynecol 218, 75-87, doi:10.1016/j.ajog.2017.05.067 (2018).
- Eller, A. G. et al. Maternal morbidity in cases of placenta accreta managed by a multidisciplinary care team compared with standard obstetric care. Obstet Gynecol 117, 331-337 (2011).
- Shamshirsaz, A. A. et al. Maternal morbidity in patients with morbidly adherent placenta treated with and without a standardized multidisciplinary approach. Am J Obstet Gynecol 212, 218 e211-219, doi:10.1016/j.ajog.2014.08.019 (2015).