Validation of a comorbidity index for use in obstetric patients: A nationwide cohort study

Abstract

Introduction A previously developed Obstetric Comorbidity Index has been validated in highly selected cohorts. Validation of the index in an unselected population as well as in other health registers is, however, of high importance to determine external validity. Material and methods Using nationwide registers, we formed a nationwide cohort including completed pregnancies (both live‐ and stillborn) in Denmark from 2000 through 2014. Maternal age and 20 comorbid conditions were assessed and weighted. Outcomes were maternal end‐organ injury or death within 30 days postpartum. The index's predictive and discriminative ability was estimated by Brier score and the area under the receiver operating characteristic curve (AUC), respectively. Logistic regression analysis was used to estimate odds ratios (OR) with 95% confidence interval (CI). Results In 876 496 completed pregnancies by 527 079 women, 1.40% (n = 12 314) experienced an outcome. The majority of women (64.1%) did not have any record of a condition included in the index and only 0.3% (n = 3044) had a score >6. The incidence of an outcome increased with increasing comorbidity score from 0.9% (95% CI 0.8‐0.9) in women scoring 0% to 10.4% (95% CI 7.6‐13.9) in women scoring 9‐10. Compared with women scoring 0, a score of 1‐2 yielded an OR of 2.34 (95% CI 2.25‐2.44), 3‐4 an OR of 5.16 (95% CI 4.81‐5.54), 5‐6 an OR of 4.84 (95% CI 4.31‐5.44), and 8‐9 an OR of 7.97 (95% CI 6.54‐9.72) for experiencing the outcome. The index had a Brier score of 0.01 and an AUC of 0.64. Conclusions Despite potential weaknesses in the outcome definition, the Obstetric Comorbidity Index showed a moderate ability to discriminate and predict end‐organ injury and death in a nationwide cohort in Denmark, in accordance with previous findings. These results suggest that the index may be a useful tool to control for confounding in health research and clinically to identify women at high risk for adverse maternal outcomes.

High-risk pregnancies and their association with severe maternal morbidity in Nepal: A prospective cohort study

“…Three studies conducted in Canada, Denmark, and the United States each used the obstetric comorbidity index retrospectively in huge sample sizes. All had consistent findings of an increased risk of severe maternal outcomes with every one-point increase in the obstetric comorbidity index [59][60][61]. A study conducted in Canada found that the presence of major preexisting conditions increased women's risk of SMM six-fold [62].…”

“…These were similar to that of the current study. Studies in Canada and Denmark using the same obstetric comorbidity index showed areas under the curve of 64% [59] and 70% [61]. In Turkey, where the Knox scoring system was used, the area under the curve on admission was 65%, while at the onset of labor, it was 94% [45].…”

Pregnancy-Associated Extracorporeal Membrane Oxygenation in the United States

“…The presence of comorbid conditions which might confound the association between pregnancy status and outcome were identified by adaptation of a validated obstetricspecific comorbidity index to exclude obstetric-specific comorbid conditions (e.g., preeclampsia), and by adjustment of criteria developed for an international version of ICD-10 for the United States implementation. 9,10 Diagnosis and procedural coding were similarly used to identify potential indications for ECMO deployment (such as acute respiratory distress syndrome, heart failure, pulmonary hypertension, and amniotic fluid embolism). Outcomes analyzed included in-hospital mortality from index hospital stay, length of stay, total estimated hospital charges and costs and an occurrence of thromboembolic or bleeding complication.…”

Critical Care in Obstetrics: A Strategy for Addressing Maternal Mortality

“…The tool was validated in a prospective study by Easter et al1 which confirmed that the higher the score the greater the association with need for ICU level care. Two other recent studies were cited from Denmark2 and the United States3 which further confirmed the validity of OB-CMI as an excellent tool to predict maternal morbidity and mortality.…”