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).