Mapping Preeclampsia Risk Thresholds to Screen-Positive Rates in Routine First-Trimester Screening: A Single-Centre Audit

Background/Objectives: First-trimester screening for preeclampsia (PE) with the Fetal Medicine Foundation (FMF) competing-risks algorithm assigns each pregnancy a numeric risk (1:X), which is compared against a threshold to decide aspirin eligibility. What proportion of a real-world screened population a given numeric threshold actually selects—its screen-positive rate (SPR)—depends on which markers were available and on the population’s underlying risk distribution, independently of how well that threshold detects PE. We audited this relationship directly from routine data from a single centre.

Methods

Retrospective cohort of 5493 singleton pregnancies with a first-trimester PE risk calculated at 11–14 weeks (2020–2026) in one Romanian fetal-medicine centre. Pregnancies were stratified into five groups according to which markers were available at screening (maternal factors ± biochemistry [PAPP-A] ± uterine artery pulsatility index [UtA-PI] ± mean arterial pressure [MAP]), and the centre-specific SPR at fixed risk thresholds and the risk threshold corresponding to fixed SPR targets of 5%, 10%, 15% and 20% were computed for each group. The operational clinical threshold (1:150 before and 1:100 after the introduction of systematic MAP measurement in October 2023) was benchmarked against this map. Outcome ascertainment was quantified to determine whether these data could support any estimate of detection performance.