Overall cohort
In the overall cohort (n=634,290), variables significantly associated
with end-organ injury or death included maternal age, low income, world
region of origin, high BMI, pre-existing medical conditions, and
placental disorders (Table S4), which contributed to the final model.
Attendance at a first-trimester antenatal visit and parity were
inversely associated with the composite outcome. The corresponding model
C-statistic was 0.68 (95% CI 0.66-0.69) (Figure 1). There was minimal
overfitting of the model, with mean optimism of 0.0055 (95% CI
0.0050-0.0061), and an optimism-corrected C-statistic of 0.67 (95% CI
0.66-0.68). Model discrimination was unchanged when BMI was included. We
tested 300 pairwise interactions, of which 13 interactions were
statistically significant. The main model including interaction terms
resulted in similar model discrimination as the main model (C-statistic
0.69, 95% CI 0.68-0.70), however this model included unstable
estimates. Therefore, the model without interaction terms was chosen as
the most balanced and efficient model.
All-cause mortality from birth until 365 days postpartum occurred in 194
women over the study time period (0.3 per 1,000). The final
multivariable model for all-cause mortality no longer retained world
region of origin, parity, previous spontaneous abortion, and several
medical comorbidities (Table S5). Major psychiatric conditions and
alcohol and substance use newly emerged as predictors. The corresponding
C-statistic was 0.70 (95% CI 0.66-0.74) (Figure S2). However, this
model was slightly over-fitted, and the optimism-corrected C-statistic
was 0.67 (95% CI 0.63-0.71).
The risk classification table for the main model, dividing the cohort
according to the five categories of predicted risk of acute end-organ
injury or death (Table 2) demonstrated the capacity of this model to
classify women who are at very low risk (-LR 0.41, 95% CI 0.33-0.52)
and those at very high risk of the outcome (+LR 8.58, 95% CI
7.32-10.05), but was less useful in classifying women in intermediate
risk categories.