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ACOG, SMFM Say Conventional Screening Still 'Most Appropriate' for General Obstetric Population

NEW YORK (GenomeWeb) – Patients of any risk group may choose noninvasive cell-free DNA-based prenatal screening for common aneuploidies, but conventional screening methods "remain the most appropriate choice" for most pregnant women in the general population, according to a new committee opinion by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine.

In addition, NIPT should not be used to screen for microdeletion syndromes routinely and is not recommended for women with multiple gestations, according to the organizations.

The new recommendations, released online on the ACOG website last week, replace an earlier opinion from the committee, published in late 2012, which stated that cell-free DNA testing should not be offered to low-risk women or women with multiple gestations. 

While not endorsing the routine use of NIPT in all pregnant women, the six-page document acknowledges that technology for cell-free DNA analysis is changing rapidly, and that "any recommendations regarding its use in screening also will likely evolve quickly."

According to the report, studies have shown that the sensitivity and specificity of cell-free DNA testing is similar in the general obstetric population and in high-risk women. However, because aneuploidy is less common in general pregnancies, the positive predictive value is lower, meaning there will be more false positive test results than in high-risk pregnancies.

In addition, traditional serum analyte screening methods pick up additional chromosomal abnormalities and other issues that NIPT cannot detect.

"Given the performance of conventional screening methods, the limitations of cell-free DNA screening performance, and the limited data on cost-effectiveness in the low-risk obstetric population, conventional screening methods remain the most appropriate choice for first-line screening for most women in the general obstetric population," the authors wrote.

Microdeletion screening, which is offered by some NIPT providers, has not been validated in clinical studies, they noted, so its sensitivity and specificity is unknown and screening for microdeletion syndromes "should not be performed" routinely.

With regards to twin pregnancies, while early data suggest that cell-free DNA screening is accurate, "larger prospective studies and published data are needed before this method can be recommended for multiple gestations," they wrote.

Women with a "no call" NIPT result should receive counseling and be offered ultrasound or diagnostic testing because their risk of aneuploidy is increased.

In general, patients undergoing cell-free DNA screening should be counseled about the limitations of the test, both in terms of its accuracy and the conditions it covers, and decisions such as pregnancy termination should not be based on the results of NIPT alone.

Also, patients should still be offered maternal serum alpha-fetoprotein screening or an ultrasound to assess the risk of other fetal anomalies, such as neural tube defects or ventral wall defects.

While the use of multiple aneuploidy screening methods is "not cost-effective," cell-free DNA screening "is reasonable" as a follow-up test for patients with a positive conventional screening result, the committee said.