INTRODUCTION
Preeclampsia (PE) and small for gestational age (SGA) are the main complications of placental disease. First-trimester PE screening using algorithms that include a combination of maternal characteristics, biophysical markers (mean arterial blood pressure (MAP) and mean uterine artery pulsatility index (UtAPI)), and biochemical markers (placental growth factor (PlGF) and pregnancy-associated plasma protein-A (PAPP-A)), can accurately predict PE and SGA1–4. The Fetal Medicine Foundation (FMF) and Gaussian algorithms can identify 80-90% of pregnant women who will develop PE with delivery <32/<34 weeks of gestation (weeks)1,5 and 60-70% of women who will develop PE with delivery <37 weeks1,6, at a 10% false positive rate (FPR). These algorithms can also predict 50-60% of SGA with delivery <32 weeks and 30-40% of SGA with delivery <37 weeks2,4.
Despite the FMF algorithm is the most used and validated worldwide, the Gaussian algorithm has some features that confer advantages in the clinical practice, reason why it is being used for routine first-trimester PE screening in most maternities across Spain since 2018. Firstly, blood sample for measurements of biochemical markers (PAPP-A and PlGF) is drawn between 8+0 weeks and 13+6 weeks as with routine aneuploidy screening (allowing the use of a two-step approach and immediate PE risk calculation at the first-trimester scan)6. Secondly, UtAPI assessment can be done both transabdominally and transvaginally, rendering the algorithm more versatile to different clinical settings. Thirdly, likelihood ratios for the a priori risk calculation were not derived from the study population in which the algorithm was investigated, but from a larger meta-analysis that included more than 25,000,000 pregnancies7. This may render the Gaussian algorithm less overfitted to a given population and, therefore, more adaptable for populations with different characteristics.
The FMF algorithm has been developed and prospectively validated in large populations, showing comparable predictive performances to the original study8–12. By contrast, the Gaussian algorithm has been investigated only in a single cohort of participants. In the past few years, routine PE screening has been implemented in most hospitals, leaving virtually no women at a high risk for PE without aspirin treatment to prospectively assess the external validity of the Gaussian algorithm. Therefore, an indirect approach to test the performance of the Gaussian algorithm is to compare it with the most externally validated combined screening tool for PE worldwide: the FMF algorithm.
The aim of this study was to compare the predictive accuracy for PE and SGA of the Gaussian and FMF algorithms.