The obstetrics comorbidity index as a predictive tool for risk-appropriate maternal care

Background: The aim of this study was to assess the correlation between obstetric co-morbidity index (OBCMI) and severe maternal morbidity (SMM) in antepartum obstetrics transfers. By utilizing a population of transfers to a level IV maternal care facility, we hope to demonstrate validity for the use of OBCMI in the triage of transfer to provide risk-appropriate maternal care.

Methods: Antepartum obstetrics transfers to a single level IV maternal care facility from 1/1/2016 to 12/31/2020 that resulted in delivery during the same encounter were included in this retrospective study. The components of the OBCMI score were retrospectively collected by manual chart review of transfer and admission notes in the electronic medical record (EMR). SMM was determined via ICD-10 and CPT code extraction from time of transfer through six weeks postpartum and confirmed by the same reviewer. Mode of delivery, length of stay, ICU admission, readmission and reoperation were obtained via institutional databases and manual EMR review.

Results: Among 561 transfers meeting the inclusion criteria, the median OBCMI was significantly higher for transfers with a maternal-only indication (n = 232) compared to fetal-only( n = 282) (median [IQR], 6 [4-8], 5 [4-6], and 1 [0-2] for maternal-only, maternal-fetal combined (n = 47), and fetal-only; p < 0.001). The prevalence of SMM was 16.8% (39/232), 27.7% (13/47), 2.1% (6/282), p < 0.0001 for those transferred for maternal, fetal and maternal, and fetal only indications respectively. The median (IQR) OBCMI score was 5 (4-8) and 3 (1-5) for those with versus without SMM. A cut-off OBCMI score of ≥ 4 was identified with 81% sensitivity (95% CI 68.6-90.1%) in predicting SMM (P = < .0001) and was noted to be significantly associated with operative delivery, blood transfusion, ICU admission, prolonged hospitalization, and reoperation. Using a cut-off OBCMI score of ≥ 4 on the population transferred for maternal and maternal-fetal combined indications only (279) yielded a specificity of 90.4% and sensitivity of 23.8% (p = 0.024).

Conclusion: OBCMI was demonstrated to discriminate for SMM in a population of obstetrics transfers to a Level IV maternal care facility. When stratifying for maternal indicated transfers, the ability of OBCMI as a predictive tool decreased. The obtained cutoff OBCMI value of ≥ 4 had high specificity but may miss a significant population that would benefit from transfer. Use of the OBCMI may be too crude of a measure to provide a comprehensive risk assessment to predict SMM and adverse obstetrics outcomes. Further studies that may include newer tools such as machine learning may be necessary to develop a more clinically useful tool.