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.