(585) Obstetrics comorbidities index predicts severe maternal morbidity in patients with placenta accreta spectrum

Objective:
The obstetric comorbidity index (OB-CMI) is a clinical risk-assessment tool that prospectively identifies patients at risk of severe maternal morbidity (SMM); however, its additive utility in patients with pre-existing risk due to placenta accreta spectrum (PAS) remains unknown. We assessed the association between OB-CMI and SMM in deliveries with PAS.

Study Design:

We conducted a retrospective cohort study of patients with histologically confirmed PAS delivered via cesarean hysterectomy at two major academic medical centers between 2019 and 2024. The primary outcome was number of SMM events based on ACOG/SMFM consensus definition, excluding hysterectomy. We additionally stratified analysis by cesarean urgency and histopathologic PAS grade. OB-CMI was calculated by the patient’s primary nurse. Given the increased risk of SMM in patients with scores >9 in prior studies, we similarly stratified our results to reflect this risk threshold. Chi-square testing was used to assess the association between OB-CMI and SMM. 


Results:
A total of 72 cases were identified, of whom 61 (85%) experienced severe maternal morbidity (Table 1). OB-CMI ranged from 1 to 14 in the study cohort. Those with OB-CMI scores >9 had higher number of SMM events (median SMM 1 vs 1, interquartile range (IQR) 0-1 vs 1-2, P=0.057), when compared to cases with OB-CMI < 9 (Table 2). A higher number of SMM events continued to be observed in the OB-CMI score >9 group after removing blood transfusions (median SMM 0 vs 0, IQR 0-0 vs 0-1, P=0.002). With scheduled hysterectomy, OB-CMI score < 9 was associated with less non-transfusion SMM (median 0 vs 0, IQR 0-0 vs 0.5, P=0.013) compared to those with OB-CMI >9. Scheduled hysterectomy was not associated with a higher OB-CMI (7 vs 6, P=0.17). Histopathologic stage of PAS was not associated with occurrence of SMM (P=0.39).

Conclusion:
Identification of high-risk pre-existing conditions as delineated by obstetrics comorbidities index (OB-CMI) predicts severe maternal morbidity events in patients with placenta accreta spectrum when removing anticipated morbidity of blood transfusions.