New classification of placenta accreta spectrum disorders should include presence of Cesarean scar pregnancy

We read with interest the study by Abinader et al. on the diagnostic performance of first-trimester ultrasound in detecting placenta accreta spectrum (PAS) disorders1. The authors performed a retrospective case–control study comparing women undergoing Cesarean hysterectomy for PAS with those who had placenta previa without PAS. They reported that placental lacunae, an abnormal uteroplacental interface and lower uterine segment hypervascularity were more common in cases affected by PAS compared with controls. Despite the retrospective design, small sample size and lack of information on the number of prior Cesarean sections in the control group, a strength of the study is the adoption of the first-trimester classification of PAS proposed by the task force of the Society for Maternal–Fetal Medicine (SMFM)2. Importantly, this task force reports that the two principal sonographic markers for PAS diagnosis in the first-trimester consist of low implantation of the gestational sac and Cesarean scar pregnancy (CSP). In previous studies and systematic reviews, we have demonstrated that the most common sign of PAS in the first trimester of pregnancy is implantation of the gestational sac in the area of the prior Cesarean scar, which defines the presence of CSP3–5. This type of low implantation is identified more easily on early (5–9 weeks) than late (11–14 weeks) first-trimester ultrasound scan because, with advancing gestation, the upper pole of the gestational sac grows towards the uterine fundus, thus making assessment of the relationship between the gestational sac and prior Cesarean scar more challenging. The now-accepted association between CSP and PAS has shed light on the natural history of these disorders and has given rise to the diagnostic dilemma regarding the optimal timing of assessment of women at risk of such conditions. First-trimester ultrasound assessment would not improve significantly the diagnostic performance of prenatal imaging in detecting PAS, as the detection rate of ultrasound in the second and third trimesters is very high according to recent series4,5, but could theoretically allow parents to make more informed decisions regarding management of their pregnancy. Irrespective of that, SMFM’s recently proposed classification of PAS represents further confirmation that the natural history of PAS is now well-established and that CSP and PAS should be considered as the same clinical entity. We believe that future guidelines on PAS should follow the new classification proposed by the SMFM task force and include presence of a low-lying gestational sac in the diagnostic criteria. Speaking the same language would facilitate the design of standardized and homogeneous research and clinical protocols, which in turn might improve the outcome of pregnancies complicated by these anomalies.