ABSTRACT
Couples with recurrent pregnancy loss are at increased risk of fetal chromosomal abnormalities in subsequent pregnancies. Screening for chromosomal abnormalities has the simple aim of identifying pregnancies at sufficiently high risk of an affected birth to warrant the hazards and costs of invasive testing. Maternal plasma cfDNA testing is more effective in screening for Down, Edwards, and Patau syndromes compared to conventional methods; it can also be applied to sex chromosome abnormalities. In conventional screening, twins discordant for aneuploidy have biochemical marker levels intermediate between concordant and unaffected twins, so there is a reduced detection rate. The increased detection rate for Down syndrome at a considerably lower false-positive rate suggests that primary cfDNA screening should replace conventional modalities. In a sequential screening situation, lower cutoffs than used in population screening might be considered. Various marker combinations, determined concurrently, formed the basis for the first effective screening protocols.
