Cell-free DNA screening for trisomies yields reliable results overall

Use of cell-free DNA (cfDNA) testing at 10 weeks’ gestation to routinely screen for trisomies 21, 18, and 13 is achievable and it yields lower false-positive rates compared with combined testing. The downside, however, is that abnormal results must be validated by chorionic villus sampling (CVS), according to new research in the journal Ultrasound in Obstetrics & Gynecology.

The goal of the research was to measure the viability of standard maternal cfDNA testing to assess for trisomies 21, 18, and 13 at 10 weeks gestation.

The prospective study enrolled 1005 women (median maternal age: 37; range, 20-49) from the Fetal Medicine Centre in London, England, between October 2012 and April 2013 who had a singleton pregnancy and a live fetus with crown-rump length 32–45 mm. Screening for trisomies 21, 18, and 13 with cfDNA was performed at 10 weeks and a combined test was done at 12 weeks.

Trisomy risks were noted for 957 (95.2%) cases; for 98.0%, the results were obtainable 14 days after sampling. No result was given in 4.8% of cases because of laboratory-related issues, assay failure, or low fetal fraction. In 40 cases, repeat sampling was conducted; results were delivered in 67.5% of these cases. The risk score for trisomy 21 and for trisomy 18 was >99% in 11 cases and 5 cases, respectively. Risk for trisomy 13 was 34% in 1 case.

Trisomies were detected by karyotyping after CVS in all except 1 case of trisomy 18 in which the karyotype was normal. Based on maternal ages of the study population, probable and actual numbers for each trisomy were similar. The cfDNA and combined testing found all trisomies; however, the estimated false-positive rates were 0.1% and 3.4%, respectively.

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