Placenta accreta spectrum: Welcome progress and a call for
standardization.
Mini-commentary for BJOG on Kayem et al 2021 BJOG-20-1462R3
Placenta accreta spectrum (PAS) is among the most feared causes of
maternal morbidity worldwide, and yet few prospective data are available
to inform best practice. PAS is rare enough that rigorous study in a
single center is difficult, but common enough that most obstetric
hospitals now encounter PAS. Management and outcomes vary strikingly
between hospitals and best practice, regrettably, is guided more by
expert consensus than by level I evidence. In fact, most clinical
questions regarding management of PAS are informed by essentially no
prospective data (Collins et al. Am J Obstet Gynecol. 2019;220:511-526).
Into this data void has come the PACCRETA cohort (Kayem et al. Act
Obstet Gynecol Scand 2013;92:476-482) and some of its first results,
published in this issue of BJOG (Kayem et al. BJOG 2021). PACCRETA is a
prospective population-based study from 176 hospitals in France,
capturing 30% of all French deliveries, from from 2013 to 2015. The
study investigators identified 249, or 4.8 per 10,000, cases of PAS.
Of all PAS patients, Kayem and colleagues found that a full half did not
have the classic combination of risk factors for PAS (previa with
history of cesarean). This group had lower morbidity and milder disease
than those with the classic combination. Only 17% of those without
classic risk factors were diagnosed antenatally. The message here is
mixed: those without classic PAS risk factors are less likely to be
diagnosed antenatally (bad) but appear to suffer less morbidity overall
(good).
But did these patients actually have PAS? Only 21% of those without
prior cesarean and previa had a hysterectomy. Although this could be due
to a regional preference for conservative treatments, the presence of
false positives seems likely. Without a hysterectomy specimen, the
diagnosis of PAS is difficult, controversial, and (in our opinion)
highly susceptible to overdiagnosis. The authors define “strict”
criteria for true cases of PAS, but several criteria depended entirely
on the subjective assessment of a clinician faced with a difficult
placental removal and the flawed principle of PAS as diagnosis of
exclusion . Difficulty in manual placental removal or massive bleeding
from an implantation site does not always indicate that microscopic PAS
was present. Similarly, areas of prior cesarean section scar dehiscence
(windows) where the placenta can be seen through the serosa are often
diagnosed as percreta (Figure) without any histological evidence of the
villous tissue having invaded through the serosa or beyond (Hecht et al.
Modern Pathol 2020;33:2382-2396).
We congratulate Kayem and colleagues for the current study and all of
their important contributions to our understanding of PAS. However,
these data illustrate the need for standardization of the definition of
PAS, especially in conservatively managed cases with considerable
potential for misdiagnosis. There is a desperate need for controlled
studies of patients with antenatally suspected PAS with detailed and
objective documentation of imaging, intra-operative findings, and when
available, histopathological examination. In absence of such studies,
the void of definitive data to guide treatment options will remain wide
open.