30 CHAPTER 2 indicate better fit of the model to the data. We also considered the fit-indices’ relative decrease, as done in previous studies (29), because a continuous decrease in the AIC is common with large sample sizes and the aBIC also may indicate towards a model with more classes than useful (30). We additionally reviewed the models’ entropy, which reflects how clearly the classes can be distinguished with scores ranging from 0 to 1 (optimum) (31). We selected three preferred models based on their fit statistics and compared their item-response probabilities. The final model was selected based on parsimony and interpretability and women were classified into one of the identified classes based on predicted class membership (largest posterior probability). Further, to evaluate the LCA’s robustness, we performed two additional analyses. First, to unravel the impact of previous pregnancies, we excluded nullipara and conducted a LCA with additionally previous perinatal and pregnancy outcomes. Second, to evaluate whether similar vulnerability classes can be distinguished across women in the entire reproduction age, we repeated the LCA with a different study population consisting of all women between 19 and 44 years old. Regression analysis We studied the association between class membership and adverse outcomes by means of unadjusted logistic regression analysis. Results are reported as odds ratios (ORs) with 95% confidence interval (CI). A p-value of <0.05 was considered statistically significant. RESULTS The study population consisted of 4172 women, of whom 1129 had missing data (Table 1). A five-class model was considered best (see Appendix 3 for fit-indices). The aBIC reached a minimum in the 12-class model, but did not show considerable improvement after models beyond seven classes when reviewing the relative fit (elbow shape). The AIC continuously decreased as expected. Entropy values were regarded best for models with two to five classes. We compared the interpretation of models with four, five and six classes and chose the five-class model for its interpretative and distinctive classes.
RkJQdWJsaXNoZXIy MTk4NDMw