With Rapid Expansion of NIPT Use Come Calls for More Informed Testing Choice

The rapid uptake in noninvasive prenatal testing (NIPT) is unprecedented in molecular testing and represents an early success story for migrating sequencing-based testing into the clinical setting. As the number of women of advanced maternal age continues to increase, NIPT for cell-free fetal DNA has emerged as an increasingly preferred screening tool for the detection of aneuploidy in these high-risk patients. Now that NIPT is gaining traction, data is emerging on the tests’ performance in actual clinical practice as well as some concerns regarding the need for improved counseling prior to testing. As might be expected, a review of the University of North Carolina (Chapel Hill; UNC) Prenatal Diagnosis unit’s initial experience with NIPT showed an increase in NIPT uptake accompanied by a significant decline in amniocentesis procedures, according to a case study published in the September issue of Genetics in Medicine. However, the rates of “unclassified,” false-positive, and false-negative results reported to UNC were higher than anticipated based on published preclinical trials, the authors say, who also noted decreased success of the test in obese patients. Over the study period (January to September 2012) the center tested 280 women using NIPT. Screening criteria included patients with a gestational age of at least 10 weeks with advanced maternal age (35 years or older for single pregnancy or 32 years or older for twins), abnormal ultrasound findings, or a positive first- or second-trimester serum screen. The majority of tested patients had advanced maternal age (71.2 percent). Samples were tested at either Sequenom or Verinata Health. An abnormal noninvasive prenatal test (either positive for aneuploidy or “unclassified” result) was reported in a combined 6.3 percent of patients (13 of 208 women). For detection of trisomies 21, 18, and 13, NIPT had a combined sensitivity of 87.5 percent and specificity of 99.5 percent. Additionally, there was one false-positive result seen for monosomy 18/trisomy 13 with a subsequent normal karyotype and microarray, but this abnormal NIPT result is believed to be related to metastatic maternal cancer detected postpartum. Only Verinata reported unclassified results (five of 45 patients). Among these unclassified patients, poor pregnancy outcomes included two unexplained fetal demises and one karyotype-confirmed trisomy 18. NIPT results were not reportable due to a below-threshold fetal fraction in three obese patients. Over the study period, the number of patients requesting noninvasive prenatal testing increased monthly. Simultaneously, the rate of amniocenteses significantly declined (8.1 percent before NIPT versus 5.3 percent after). There were no significant changes in the rates of chorionic villus sampling (CVS) or first-trimester combined screens with the introduction of NIPT. The authors emphasize that invasive screening (amniocentesis or CVS) or postnatal karyotyping is still recommended as follow-up to abnormal or unclassified NIPT results and with abnormal ultrasound, even with a negative NIPT results. “Two of these patients with normal NIPT and [ultrasound] anomalies went on to deliver neonates diagnosed with genetic syndromes, 22q11.2 deletion syndrome and a rare single-gene disorder,” write the authors, led by Carmen Beamon, M.D. “This highlights the importance of reinforcing the fact that this technology screens for a limited number of aneuploidies and that patients and providers should not be falsely reassured by normal NIPT results in the setting of anomalies.” Yet follow-up invasive prenatal diagnostic testing is not “universally accepted,” the authors say, with only 61 percent of UNC patients with an abnormal NIPT undergoing invasive testing. Other researchers have seen similar findings, raising concerns about pretest counseling, women’s understanding of potential NIPT results, and whether or not such testing is understood to be voluntary rather than required, routine testing. The Need to Better Inform Testing Options Researchers from the University of California, San Francisco (UCSF), say that although the technology for prenatal testing has evolved rapidly, there is a gap in understanding women’s personal interest and preferences for available prenatal tests. The UCSF group says that use of a computerized, interactive decision-support guide can promote preference-based decisions and fully informed choices about prenatal testing options, including the option to forgo testing, according to a study published Sept. 24 in the Journal of the American Medical Association. “The recent introduction of cell-free DNA testing has intensified the complexity of prenatal testing decision making, generating concerns about the potential for erosion of informed choice,” write the authors, led by Miriam Kuppermann, Ph.D. The researchers conducted a trial in which prenatal clinic patients (of varying literacy) were randomized to either a computerized, interactive decision-support guide (lasting 45 minutes to one hour) with access to free prenatal testing (n = 357) or usual care as per current guidelines (n = 353). The researchers found that women in the intervention group were significantly less likely to have invasive diagnostic testing and were more likely to forgo testing altogether, although they had higher knowledge scores (more likely to correctly estimate the amniocentesis-related miscarriage risk and their estimated age-adjusted chance of carrying a fetus with trisomy 21). “This study’s finding that women who were randomized to the intervention group were less likely to undergo testing than those who received usual care adds support to the contention that women may not be receiving adequate counseling about their options,” conclude the authors. “With the advent of cell-free DNA testing for aneuploidy, it is particularly important that women understand the purpose and potential consequences of undergoing testing, as without adequate counseling, this new test may easily come to be viewed as simply another blood test in the large panel of routine prenatal laboratories.” The authors do caution that while no information on NIPT was included in the decision-support guide nor was the test available to study participants, “the general features of cell-free DNA testing and the conditions for which it screens are similar to the tests covered in this study, and the implications for counseling and informed patient decision making remain the same.” Takeaway: The uptake in NIPT is unprecedented in molecular diagnostics. But with this shifting paradigm in prenatal testing comes concern over understanding of the positive predictive value of commercially available tests, as well as patients’ awareness of testing’s downstream implications. Side Box: Predictive Ability of NIPT May Be Overstated The positive predictive value (PPV) of NIPT may be overstated when results are compared to conventional cytogenetics, according to a study published online Aug. 7 in Genetics in Medicine. Researchers from Quest Diagnostics conducted a review to determine the concordance of results between 109 consecutive cases referred for confirmation of NIPT results with cytogenetic studies (prenatal and/or postnatal studies using karyotyping, fluorescence in situ hybridization, and/or oligo–single-nucleotide polymorphism microarray). All four NIPT providers (Natera, Ariosa Diagnostics, Sequenom, and Illumina) were represented, and positive NIPT results included trisomy 21 (41 cases), trisomy 18 (25 cases), trisomy 13 (16 cases), sex chromosome aneuploidy (16 cases), trisomy 16 (three cases), monosomy 21 (two cases), and one case each of triploidy and microdeletion of 22q11.2. Four cases of negative NIPT results, but with positive ultrasound findings, were also included. Cytogenetic results yielded a true-positive rate of 93 percent for NIPT trisomy 21 results, 64 percent for trisomy 18, 44 percent for trisomy 13, and 38 percent for sex chromosome aneuploidy. Six cases with positive NIPT results for monosomy 21, trisomy 16, triploidy, or 22q11.2 microdeletion had normal cytogenetic findings. One false negative for NIPT was identified in nonmosaic trisomies 9 and 21. The Quest data, combined with NIPT data from two independent groups, yields a PPV of 94.4 percent for cases positive for trisomy 21 by NIPT but is significantly lower for trisomy 18 (PPV = 59.5 percent), trisomy 13 (44.4 percent), and sex chromosome aneuploidy (37.9 percent). The authors say their dataset was not large enough to differentiate PPV among the four NIPT laboratories. “The PPV for any test is proportional to the specificity of the assay and the prevalence of the disorder. It is very important to perceive that PPV is not intrinsic to the test,” write the authors, led by Jia-Chi Wang, M.D., Ph.D., from the Quest Diagnostics Nichols Institute in San Juan Capistrano, Calif. The authors urge careful interpretation of NIPT results and better education of providers. “The ability of NIPT to correctly predict a positive result for trisomy 18 and trisomy 13 is less than 60 percent,” write the authors. “For this reason, it is crucial that providers and consumers understand that NIPT is fundamentally a screening test and cannot be used as a replacement for invasive prenatal diagnosis.”