be used to confirm a positive maternal screening test such as a first trimester screening or ultrasound markers of the condition. trisomy 13 and 18 analysis of cffdna from maternal plasma with mpss looking for trisomy 13 or 18 is possible factors limiting sensitivity and specificity include the levels of cffdna in the maternal plasma; maternal chromosomes may have mosaicism. a number of fetal nucleic acid molecules derived from aneuploid chromosomes can be detected including serpineb2 mrna, clad b, hypomethylated serpinb5 from chromosome 18, placenta-specific 4 (plac4), hypermethylated holocarboxylase synthetase (hlcs) and c21orf105 mrna from chromosome 12. with complete trisomy, the mrna alleles in maternal plasma isn't the normal 1:1 ratio, but is in fact 2:1. allelic ratios determined by epigenetic markers can also be used to detect the complete trisomies. massive parallel sequencing and digital pcr for fetal aneuploidy detection can be used without restriction to fetal-specific nucleic acid molecules. (mpss) is estimated to have a sensitivity of between 96 and 100%, and a specificity between 94 and 100% for detecting down syndrome. it can be performed at 10 weeks of gestational age. one study in the united states estimated a false positive rate of 0.3% and a positive predictive value of 80% when using cffdna to detect down syndrome. preeclampsia preeclampsia is a complex condition of pregnancy involving hypertension and proteinuria usually after 20 weeks gestation. it is associated with poor cytotrophoblastic invasion of the myometrium. onset of the condition between 20 and 34 weeks gestation, is considered "early". maternal plasma samples in pregnancies complicated by preeclampsia have significantly higher levels of cffdna that those in normal pregnancies. this holds true for early onset preeclampsia. future perspectives new generation sequencing may be used to yield a whole genome sequence from cffdna. this raises ethical questions. however, the utility of the procedure may increase as clear associations between specific genetic variants and disease states are discovered.