Assessment of placenta accreta spectrum at vaginal birth after cesarean delivery.

BACKGROUND: Prior cesarean delivery is a risk factor for developing placenta accreta spectrum (PAS) in a subsequent pregnancy and patients with antenatally suspected PAS frequently undergo planned cesarean hysterectomy. There is a paucity of data regarding unsuspected PAS among patients undergoing trial of labor after cesarean for attempted vaginal birth after cesarean delivery (VBAC).

OBJECTIVE: The purpose of this study was to investigate the incidence, characteristics, and delivery outcomes of patients with PAS diagnosed at the time of VBAC.

STUDY DESIGN: The Healthcare Cost and Utilization Project's National Inpatient Sample was retrospectively queried to examine 184,415 patients with a history of low-transverse cesarean section who had vaginal delivery in the current index hospital admission between 2017-2020. Those with placenta previa, prior vertical cesarean section, other uterine scar, and uterine rupture were excluded. We identified PAS cases using the World Health Organization's International Classification of Disease, 10th revision codes of O43.2. Co-primary outcomes were (i) the incidence rate of PAS at VBAC, (ii) clinical and pregnancy characteristics related to PAS, assessed with multivariable binary logistic regression model, and (iii) delivery outcomes associated with PAS by fitting propensity score adjustment. The secondary outcome was to conduct a systematic literature review utilizing three public search engines (PubMed, Cochrane, and Scopus). Data on incidence rate and maternal morbidity related to PAS at VBAC were evaluated.

RESULTS: The incidence rate of PAS at VBAC was 8.1 per 10,000 deliveries. The majority of PAS cases were placenta accreta (83.3%). In a multivariable analysis, older maternal age, tobacco use, pre-eclampsia, multifetal gestation, fetal anomaly, preterm premature rupture of membrane, chorioamnionitis, low-lying placenta, and preterm delivery were associated with an increased risk of PAS (all, P<0.05). Of these factors, low-lying placenta had the largest odds for PAS (526.3 vs 7.3 per 10,000, adjusted-odds ratio 35.02, 95% confidence interval 18.19-67.42). Patients in the PAS group were more likely to have postpartum hemorrhage (80.0% vs 5.5%), blood product transfusion (23.3% vs 1.0%), shock or coagulopathy (20.0% vs 0.2%), and hysterectomy (43.3% vs <0.1%) compared to those without PAS (all, P<0.001). In a systematic literature review, a total of 212 studies were screened and none of these studies examined the incidence and morbidity of PAS at VBAC.

CONCLUSION: This nationwide assessment suggests that although PAS with VBAC is uncommon (1 in 1,229 cases), the diagnosis of PAS at VBAC is associated with significant maternal morbidity. The data also suggests that low-lying placenta in the setting of prior low-transverse cesarean section warrants careful evaluation for possible PAS prior to a trial of labor. These findings warrant further research to validate this study.