Abstract
Objectives: To assess whether adding placental growth factor
(PlGF) or replacing pregnancy-associated plasma protein-A (PAPP-A)
improves the first trimester combined test performance for trisomy 21.
Design: Prospective observation Cohort
Setting: The Chinese University of Hong Kong, China
Sample: 11,518 women having a singleton pregnancy screened for
trisomy 21 between December 2016 and December 2019 using the first
trimester combined test.
Methods: PlGF was prospectively measured and estimated term
risk for trisomy 21 was calculated by 1) replacing PAPP-A with PlGF and
2) adding PlGF to the combined test which includes nuchal translucency,
PAPP-A and free β-human chorionic gonadotropin (hCG).
Main Outcome Measure: Screening performance, area under curve
(AUC), detection rate (DR), screen positive rate (SPR) and false
positive rate (FPR)
Results: 29 women had trisomy 21. The combined tests DR, FPR
and SPR were 89.7%, 5.7% and 6% respectively. DR when replacing
PAPP-A or adding PlGF to the combined test remained unchanged. Replacing
PAPP-A by PlGF increased FPR and SPR to 6.2% and 6.4% respectively.
Adding PlGF to the combined test gave FPR and SPR rates of 5.5% and
5.7% respectively. Adding or replacing PlGF did not give a significant
increase in AUC (p>0.48) over that of the combined test.
Conclusion: Adding PlGF to the combined test or replacing
PAPP-A with PlGF in the combined test did not improve trisomy 21
detection rate. Replacing PAPP-A by PlGF increased SPR, whilst adding
PlGF resulted in only a marginal reduction in SPR.