In vivo model to determine fetal-cell enrichment efficiency of novel noninvasive prenatal diagnosis methods

Objective: To develop an in vivo model to determine fetal-cell enrichment efficiency of novel noninvasive prenatal diagnosis methods. Methods: Efficiency of our three-step enrichment protocol was determined in vitro before fetal nucleated red blood cells (FNRBCs) were enriched from first-trimester maternal blood samples collected from the same patients pre- and postsurgical termination of pregnancy (TOP) (n = 10). FNRBCs enriched were identified using embryonic ε-globin immunocytochemistry and chromosomal fluorescence in situ hybridization. Results: We recovered 37% of spiked FNRBCs (95% confidence interval (CI) 28.5-45.6; n = 8) in in vitro experiments. We show a consistent threefold increase in the number of ε+ FNRBCs in maternal blood obtained immediately post-TOP (p = 0.005). A mathematical relationship was derived: observed number of pretermination primitive FNRBCs = 0.6 + 0.31 (coefficient between pretermination/post-termination primitive FNRBCs, 95% CI 0.12-0.49; p = 0.005) x observed number of post-termination primitive FNRBCs (R² = 0.65). Conclusion: Our data demonstrate that maternal blood obtained immediately post-TOP would be a good in vivo model to determine the enrichment efficiency of novel protocols and methods for noninvasive prenatal diagnosis.