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Noninvasive prenatal screening for patients with high body mass index


Women with high body mass index (BMI) tend to have reduced fetal fraction (FF) during cell-free DNA-based noninvasive prenatal screening (NIPS), causing test failure rates up to 24.3% and prompting guidelines that recommend aneuploidy screening other than NIPS for patients with significant obesity. Since alternatives to NIPS are only preferred if they work better, scientists from Myriad Women's Health, California, USA, compared the corresponding efficacy of traditional screening of aneuploidy and NIPS at different levels of BMI.

«The sensitivity of NIPS is not constant for all pregnancies; rather, the ability to detect aneuploidy scales with the proportional share of fetal-derived cfDNA in the maternal plasma (i.e., the “fetal fraction” or “FF”). Many NIPS laboratories fail samples below a set FF threshold due to concerns about reporting false negatives as a result of diminished sensitivity. However, low-FF performance is both platform- and laboratorydependent: modeled versions of the two common NIPS platforms—the whole-genome sequencing (WGS) and single-nucleotide polymorphism (SNP) methods—show that WGS has higher sensitivity for low-FF samples at a fixed specificity level».

Reports of this elevated test-failure rate prompted the American College of Medical Genetics and Genomics (ACMG) to recommend against using NIPS in patients with “significant obesity.” Despite stating that NIPS is “the most sensitive screening option,” ACMG instead recommended that such patients receive “aneuploidy screening other than NIPS,” other medical societies have not provided specific guidance about patients with high BMI. Because “significant obesity” is not well defined, this recommendation potentially means that many US patients would be treated differently based on their height and weight alone. Further, adherence to this recommendation could create inequity in patient care because of ethnicityspecific differences in the distribution of BMI.

Scientists found that the expected analytical sensitivity of WGS-based NIPS is greater than the sensitivity of traditional screening.
In addition, for each aneuploidy although sensitivity decreases with an increase in BMI, analytical sensitivity remains above 94% even for pregnants with class III obesity (BMI> 40).
In general, for some NIPS methods that have a minimum FF threshold relative sensitivity at high BMI is consistent with the recommendation for using non-DNA screening instead of NIPS. However, the data obtained also indicate that this recommendation should not be universal since the sensitivity of NIPS for different BMI varies depending on the platform and laboratory.
The authors of the study concluded that compared to traditional aneuploidy screening, individually selected NIPS has the highest accuracy in women with low FF and is the best screening option for women with a high body mass index.

The study was published in the journal Prenatal diagnosis.

Авторы: Денис Черневский. Ани Газоян


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