文献_2012-Maternal plasma DNA a major step forward in prenatal testing.pdf

57 EDITORIAL Maternal plasma DNA: a major step forward in prenatal testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J Med Screen 2012; 19:57–59 DOI: 10.1258/jms.2012.012059 Almost twenty-five years have passed since the introduction contribution to the total genome sequenced. That increase is of prenatal screening for Down’s syndrome using multiple diluted according to the proportion of fetal DNA present in markers. During that time there has been steady improve- the maternal plasma sample. For example, if the fetal frac- ment in performance and clinical acceptance worldwide. tion is 10%, then the 50% increase in the expected chromo- Such screening has been the way to best determine who, some percentage is diluted 10-fold, so that the increase among the population of pregnant women, are at the measured in the maternal plasma will be, on average, only highest risk of having an affected pregnancy and, therefore, 5% (one-tenth of the maximum 50% increase). are most appropriately offered invasive procedures (amnio- Consequently, the expected increase in the percentage of centesis and chorionic villus sampling) for karyotype analy-