What is the Best Strategy for Fetal Aneuploidy Screening?
BACKGROUND AND PURPOSE:
Multiple strategies for aneuploidy screening are currently being evaluated
cfDNA has superior performance characteristics compared to standard first trimester screening (NT + markers) but may miss fetal anatomic/chromosomal anomalies that can be initially detected on ultrasound
Kagan et al. (Ultrasound Obstet Gynecol, 2017) compared the performance of first trimester standard combined screening with an approach that uses the combination of a detailed ultrasound exam and cfDNA analysis
Prospective randomized control trial of normal first-trimester ultrasound exam at 11 to 13 weeks’ gestation (2015-2016)
Subjects were randomized into two groups of assessing aneuploidy risk
Ultrasound and cfDNA screening if ultrasound is normal
Blood was retained for standard serum markers in case the cfDNA result was inconclusive
Number of false positives in screening for trisomy 21
False positive defined as normal karyotype if risk for trisomy 21 was >1:100, irrespective of the method of risk calculation
688 women with normal first-trimester ultrasounds were randomized into each group (1) Standard screening cohort and (2) ultrasound + cfDNA cohort
All 7 cases of DS were detected on ultrasound based on enlarged NT or fetal anomalies, as were trisomy 13 and 18 cases
When comparing risk assessment using standard screening vs ultrasound + cfDNA cohorts, there were no major demographic differences
The ultrasound + cfDNA cohort median risk for trisomy 21 was 1 in 10,000
None of the cases had a risk above 1:100 [95% CI 0.0 – 0.5%]
The standard screening cohort median risk for trisomy 21 was 1 in 3,786
> 1:100 risk was identified in 17 (2.5%) pregnancies (95% CI 1.5 – 3.9%)
A first-trimester screening for trisomy 21 using ultrasound, NT measurement, and cfDNA in women without ultrasound anomalies is associated with a significant reduction in the false positive rate compared to standard screening
This study suggests first trimester serum markers (β-hCG and PAPPA) should not be used
By including a detailed ultrasound, disadvantages of cfDNA only testing only are overcome
Anatomic assessment provided by ultrasound
Saving blood for markers if necessary can address the problem of inconclusive cfDNA results
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