Clinical Perspective of Cell-Free DNA Testing for Fetal Aneuploidies

Abstract

Cell-free DNA testing in maternal blood provides the most effective method of screening for trisomy 21, with a reported detection rate of 99% and a false positive rate of less than 0.1%. After many years of research, this method is now commercially available and is carried out in an increasing number of patients, and there is an expanding number of conditions that can be screened for. However, the application of these methods in clinical practice requires a careful analysis. Current first-trimester screening strategies are based on a complex combination of tests, aiming at detecting fetal defects and predicting the risk of main pregnancy complications. It is therefore necessary to define the optimal way of combining cell-free DNA testing with current first-trimester screening methods. In this concise review we describe the basis of cell-free DNA testing and discuss the potential approaches for its implementation in combination with current tests in the first trimester.

Cell-Free DNA Analysis in Maternal Blood: Differences in Estimates between Laboratories with Different Methodologies Using a Propensity Score Approach

“…DANSR also evaluates SNPs to estimate the FF in the same assay. This approach should therefore lead to reduced costs, because the number of regions that need to be analyzed is substantially lower than for whole-genome sequencing [17]. In GW-MPS, molecules from all chromosomes are examined with the potential to identify all aneuploidies.…”

“…In GW-MPS, molecules from all chromosomes are examined with the potential to identify all aneuploidies. However, since chromosome 21 represents only approximately 1.5% of the human genome, it is necessary to sequence millions of molecules from the complete genome to ensure sufficient chromosome 21 counts for a differentiation between trisomy 21 and euploid pregnancies [17]. To our knowledge, no between-laboratory comparisons of cfDNA testing using different methodologies have been reported.…”

“…Several factors associated with uninformative cfDNA results or a low FF have been identified, such as maternal weight, a low level of pregnancyassociated plasma protein A, twin pregnancy, and conception by in vitro fertilization (IVF) [15,16]. So far, 3 approaches for the analysis of cfDNA in maternal blood have been used in clinical studies: genome-wide massively parallel sequencing (GW-MPS) and targeted (chromosome-selective) methods based on digital analysis of selected regions of polymorphic as well as nonpolymorphic loci by massively parallel sequencing or array technology (DANSR TM ) or based on assessment of single nucleotide polymorphisms (SNPs) [17,18]. It is therefore possible that the various methods used for cfDNA analysis could also influence the performance and no-result rate of the test; however, apart from case reports, comparisons of results stemming from different laboratories have not yet been made.…”

Impact of Including or Removing Nuchal Translucency Measurement on the Detection and False-Positive Rates of First-Trimester Down Syndrome Screening

“…Recent evidence suggests that analysis of cell-free DNA in maternal blood can detect about 99% of cases of trisomy 21 with a false-positive rate of about 0.1%, with, however, two drawbacks: results lacking in 3% of cases and very high cost [24,25]. Clinical implementation of cell-free DNA testing has been discussed, contingent on the results of first-line screening using the first-trimester combined test [26]. Cell-free DNA testing could be offered to the high-risk group or to the intermediate-risk group (cut-off depending on each health policy).…”

Increased Umbilical Artery Pulsatility Index in Third-Trimester Fetuses with Trisomy 21

“…With the current change towards cell-free fetal DNA testing, the detection rate for trisomy 21 approaches 99% and the number of invasive procedures to achieve this detection has diminished dramatically [1,2,3]. …”