Unsuspected placenta accreta spectrum at vaginal delivery: assessment of incidence, characteristics, and maternal morbidity

Placenta accreta spectrum refers to morbidly adherent trophoblastic tissue invading into the gravid uterus and is associated with significant maternal morbidity. Most cases of placenta accreta spectrum are suspected antenatally, and most patients undergo planned, late-preterm cesarean hysterectomy to reduce the risk of morbidity. Rarely, however, placenta accreta spectrum is incidentally diagnosed at vaginal delivery, but there is a scarcity of data regarding these events.This study aimed to examine the incidence, characteristics, and outcomes of pregnant individuals with incidentally diagnosed placenta accreta spectrum at term vaginal delivery.This was a retrospective cohort study investigating the Healthcare Cost and Utilization Project's National Inpatient Sample. The study population was 8,694,669 term vaginal deliveries from January 2016 to December 2019. Exclusion criteria included previous uterine scar, placenta previa, and preterm delivery. Exposure was assigned by the diagnosis of placenta accreta spectrum. The main outcomes were: (1) incidence rate, (2) clinical and pregnancy characteristics, and (3) maternal morbidity related to unsuspected placenta accreta spectrum at vaginal delivery. Multivariable binary logistic regression analysis and inverse probability of treatment weighting were fitted for statistical analysis.Unsuspected placenta accreta spectrum was reported in 1 in 3797 vaginal deliveries. In a multivariable analysis, the following were associated with increased likelihood of unsuspected placenta accreta spectrum (all, P<.05): (1) patient factor with older age, (2) uterine factors such as uterine anomaly and uterine myoma, (3) pregnancy factors including early-term delivery and previous recurrent pregnancy losses, and (4) fetal factors of in utero growth restriction and demise. Of those, uterine anomaly had the greatest association with unsuspected placenta accreta spectrum (adjusted odds ratio, 6.23; 95% confidence interval, 4.20-9.26). In a propensity score-weighted model, patients in the unsuspected placenta accreta spectrum group were more likely to have hemorrhage (65.2% vs 4.1%), blood product transfusion (21.3% vs 0.6%), hysterectomy (14.9% vs <0.1%), coagulopathy (2.9% vs 0.1%), and shock (2.9% vs <0.1%) compared with those without placenta accreta spectrum. Patients in the unsuspected placenta accreta spectrum group were also more likely to receive manual removal of the placenta compared with those in the non-placenta accreta spectrum group (25.1% vs 0.6%).This study suggests that although unsuspected placenta accreta spectrum among patients undergoing term vaginal delivery is rare, it is associated with significant morbidity. The observed association between uterine anomalies and placenta accreta spectrum warrants further investigation.