Cohort study
Numeric and categorical data were expressed as median (interquartile range) and proportions, respectively. Differences in pregnancy outcomes between those without PE, those with term PE and those with preterm PE were compared by the analysis of variance or Kruskal-Wallis tests (for numeric parametric or nonparametric data) with the Bonferroni correction for post-hoc analysis. The Chi-square test was performed for categorical variables and for trend when the proportions between groups demonstrated an obvious trend.
The FMF algorithm was applied retrospectively. Pregnancies were screened based on maternal characteristics, MAP at booking and serum PAPP-A. Women with estimated risks of preterm PE of 1 in 100 or higher were considered high risk, whilst those with risks below 1 in 100 were considered low risk.  The risk cut-off of ≥1:150 for preterm pre-eclampsia resulted in a high screen-positive rate of 24% in our cohort. Therefore, a pragmatic decision was taken to reduce the cut-off to ≥1:100 with an expected screen-positive rate of between 10-15%. In addition to requiring aspirin prophylaxis, all women who are screen positive using the FMF algorithm would require third trimester fetal growth ultrasound surveillance.
As this was a retrospective and theoretical application of the FMF algorithm to a cohort that had been already screened using the NICE method, a proportion of pregnancies were high risk for the development of PE in both arms and, therefore, had been prescribed aspirin prophylaxis for the pregnancy that this data relates to. To appropriately adjust the effect size reported for incidence of preterm PE using the FMF algorithm, the assumption that aspirin would reduce the risk of preterm PE by 62%, as demonstrated in the ASPRE randomised controlled trial, was incorporated into analysis.4
Statistical analysis was performed with SPSS statistical software (version 27; SPSS Inc, Chicago, IL).