Isolation free Identification and Phenotyping of First Trimester Extravillous Trophoblasts Residing in Cervical Fluid

Preeclampsia (PE) remains difficult to predict, particularly when it manifests late in gestation. To capture early placental signals, we profiled trophoblast cells sampled from the cervix in the first trimester using mass cytometry (CyTOF). We established protocols for clinical sample storage and applied spike-in reference control cells to deliver reproducible, batch-corrected protein measurements, thereby advancing CyTOF from a discovery tool to a translational platform. Within HLA-GCD45- cells, we identified canonical CK7 extravillous trophoblasts, as well as a previously unrecognized CK7-subset, and both subsets expressed placental proteins. Expression of PAPP-A, GAL-13, and GAL-14 was significantly altered in a pilot cohort of pregnancies that subsequently developed late-onset PE, distinguishing cases from controls at both single-marker and multivariate levels. These findings reveal unexpected trophoblast heterogeneity, demonstrate that placental alterations are detectable before the development of late-onset PE, and establish cervical trophoblast profiling as a promising platform for scalable biomarker discovery and first-trimester risk assessment in placenta-mediated disorders. Impact StatementFirst-trimester trophoblasts sampled from the cervix reveal early molecular changes associated with late-onset preeclampsia, while an isolation-free, reference-normalized CyTOF workflow establishes a scalable, clinically compatible platform for biomarker discovery and multicenter-ready early risk assessment in pregnancy.