Norton 2015.

Study characteristics
Patient sampling	Study design: blinded, prospective cohort study. Participants: unselected population of pregnant women undergoing aneuploidy screening (without prior risk of fetal aneuploidy). Inclusion criteria: singleton pregnancies, at least 18 years of age, and between 10 to 14 weeks of gestation. Exclusion criteria: women who had a miscarriage, chose to terminate the pregnancy or had a stillbirth without confirmatory genetic testing.
Patient characteristics and setting	Number enrolled: 18,955 pregnant women. Number available for 2 x 2 table: 15,841 pregnant women (subgroup of 84%). Setting: 35 centres in USA States, Canada, Sweden, the Netherlands, Belgium, and Italy. Recruitment period: March 2012 to April 2013. Ethnicity: Caucasian (70.9%), Afro‐American (8.2%), Asian (10.5%), Native American (0.6%), multiracial (2.7%), other (6.7%) and missing data (0.5%). Mean gestational age (range): 12.5 (10.0 to 14.3) weeks. Mean maternal age (range): 31 (18 to 48) years whose 76% of pregnant women analysed had < 35 years old. Relevant tests carried out prior to index test: none. Language of the study: English.
Index tests	gNIPT by TMPS (DANSR assay) on Illumina HiSeq 2000 sequencer in 96‐plex. Fetal fraction DNA: amount measured but not reported. Blood samples for gNIPT were collected before reference standard. Cutpoint: not reported. Usually, Harmony™ prenatal test uses FORTE algorithm; positive if FORTE risk score ≥ 1%. Commercial test: Harmony™ Prenatal Test by Ariosa Diagnostics, Inc. The traditional screening tests (combined test at the first trimester) were also assessed. Cutpoint of combined test: 1 in 270 for T21 or 1 in 150 for T18 and T13.
Target condition and reference standard(s)	Target conditions: T21, T18 and T13. Reference standards: fetal karyotype of chorionic villi, amniotic fluid or products of conception or neonatal karyotype, neonatal clinical examination or medical record from birth.
Flow and timing	Blood samples were obtained prior to the invasive procedure (reference standard). gNIPT was a first‐tier test. 3114/18,955 samples excluded of analysis including 229 samples did not meet inclusion criteria or meet exclusion criteria, 31 had twins, 121 had unknown ovum‐donor status, 64 withdrew or were withdrawn by investigator, 384 had sample‐handling errors, 308 without standard screening test result, 488 failed sequencing and have no gNIPT result (192 for low fetal fraction DNA, 83 for non fetal fraction DNA and 213 for high assay variance or assay failures) and 1489 were lost to follow‐up.
Comparative
Aim to study	To test the hypothesis that gNIPT has better performance than standard first‐trimester screening (with measurement of nuchal translucency and biochemical analytes) in risk assessment for trisomy 21 in a large, unselected population of women presenting for aneuploidy screening. To also evaluate the performance of gNIPT and standard screening in the assessment of risk for trisomies 18 and 13.
Funding source or sponsor of the study	Study funded by Ariosa Diagnostics, Inc and Perinatal Quality Foundation.
Informations about the authors contacted	Author was contacted on: 10 February 2016. Reply received on: 11 February 2016.
Notes	This study is a clinical trial (Noninvasive Examination of Trisomy (NEXT) ClinicalTrials.gov number, NCT01511458).
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
Did the study avoid inappropriate exclusions?	No
		High	Low
DOMAIN 2: Index Test TMPS
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
If a threshold was used, was it pre‐specified?	Yes
		Low	Low
DOMAIN 2: Index Test Traditional screening tests
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
If a threshold was used, was it pre‐specified?	Yes
		Low	Low
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
		Low	Low
DOMAIN 4: Flow and Timing
Was there an appropriate interval between index test and reference standard?	Yes
Did all analysed patients receive the reference standard?	No
Were all patients included in the analysis?	No
		High