Objective To determine the effects of gestational age and maternal weight on percent fetal cell-free DNA (cfDNA) in maternal plasma and the change in fetal cfDNA amounts within the same patient over time. MethodsThe cfDNA was extracted from maternal plasma from 22 384 singleton pregnancies of at least 10 weeks gestation undergoing the Harmony TM Prenatal Test. The Harmony Prenatal Test determined fetal percentage via directed analysis of cfDNA.Results At 10 weeks 0 days to 10 weeks 6 days gestation, the median percent fetal cfDNA was 10.2%. Between 10 and 21 weeks gestation, percent fetal increased 0.1% per week (p < 0.0001), and 2% of pregnancies were below 4% fetal cfDNA. Beyond 21 weeks gestation, fetal cfDNA increased 1% per week (p < 0.0001). Fetal cfDNA percentage was proportional to gestational age and inversely proportional to maternal weight (p = 0.0016). Of 135 samples that were redrawn because of insufficient fetal cfDNA of the initial sample, 76 (56%) had greater than 4% fetal cfDNA in the sample from the second draw.Conclusion Fetal cfDNA increases with gestation, decreases with increasing maternal weight, and generally improves upon a blood redraw when the first attempt has insufficient fetal cfDNA.

ObjectiveTo evaluate the clinical performance of non‐invasive prenatal testing for trisomy 21, 18, and 13 using targeted cell‐free DNA (cfDNA) analysis.MethodsTargeted cfDNA analysis using DANSR™ and FORTE™ with microarray quantitation was used to evaluate the risk of trisomy 21, 18, and 13 in blinded samples from 799 singleton, twin, natural, and IVF pregnancies. Subjects either had fetal chromosome evaluation by karyotype, FISH, QF‐PCR, or karyotype for newborns with suspected aneuploidy at birth. The results of targeted cfDNA analysis were compared to clinical genetic testing outcomes to assess clinical performance.ResultsTargeted cfDNA analysis with microarray quantification identified 107/108 trisomy 21 cases (99.1%), 29/30 trisomy 18 cases (96.7%), and 12/12 trisomy 13 cases (100%). The specificity was 100% for all three trisomies. Combining this data with all published clinical performance studies using DANSR/FORTE methodology for greater than 23 000 pregnancies, the sensitivity of targeted cfDNA analysis was calculated to be greater than 99% for trisomy 21, 97% for trisomy 18, and 94% for trisomy 13. Specificity for each trisomy was greater than 99.9%.ConclusionTargeted cfDNA analysis demonstrates consistently high sensitivity and extremely low false positive rates for common autosomal trisomies in pregnancy across quantitation platforms. © 2015 Ariosa Diagnostics Inc. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

Obstetricians plan to increase their utilization of NIPT and expect that the majority of both high-risk and average-risk patients will be offered NIPT as an option.

We could not confirm diagnostic benefit. Further investigation of other biomarkers including placental mRNA is warranted.

Letters to the EditorCell-free DNA testing for prenatal aneuploidy assessment: analysis of professional society statementsWe read the report by Hui et al. 1 'State-wide utilization and performance of traditional and cell-free DNA based prenatal testing pathways: the Victorian Perinatal Record Linkage (PeRL) study' and believe that the study provides valuable information to inform practice recommendations and health policy. We were interested in the global perspective on clinical implementation of prenatal cell-free DNA (cfDNA) testing and reviewed practice guidelines published by international and national professional societies.Guidelines were identified using the Google search engine and the PubMed and EMBASE databases. Search terms included 'non-invasive prenatal testing', 'prenatal cfDNA', 'guidelines', 'society' and 'statement'. We also reviewed the content of the retrieved websites and documents and consulted with professional colleagues to find as many additional guidelines as possible. Searches