Ramos‐Corpas 2006.

Clinical features and settings	Routine screening
Participants	1800 participants Spain ‐ hospital fetal medicine department June 2003 to April 2004 Pregnant women Singleton pregnancies Mean age 30.1 years (15‐46 years) (SD 5.37), 18% ≥ 35 years First trimester (before week 14)
Study design	Prospective cohort
Target condition and reference standard(s)	Down’s syndrome: 7 cases Reference standards: invasive testing offered to patients considered high risk at screening (> 1:300) or follow‐up to birth
Index and comparator tests	Maternal age First trimester NT (FMF method (Accuson XP10, Mountain View, California) Maximum allotted time of 20 minutes) First trimester nasal bone assessment (in 93.4% of patients) Risk cut‐point 1:300 PAPP‐A and free ßhCG (Delfia Xpress 6000 immunoanalyzer, Perkin Elmer) ‐ not used in study Published population parameters used (Wald 2003)
Follow‐up	Follow‐up in all patients without invasive testing by 1) monitoring all births and miscarriages at the hospital, 2) continued contact with the genetics departments and 3) telephone follow‐up. States in abstract that only fetuses with complete follow‐up results included in the study
Aim of study	To evaluate the utility of determining the presence or absence of nasal bone in a low‐risk fetal population
Notes	5 cases diagnosed by invasive testing, 2 by follow‐up
Table of Methodological Quality
Item	Authors' judgement	Description
Representative spectrum? All tests	Yes	Routine screening of typical pregnant population
Acceptable reference standard? All tests	Yes	Karyotyping or follow‐up to birth
Partial verification avoided? All tests	Yes	All women received a reference standard
Differential verification avoided? All tests	No	Choice of reference standard depended on index test results
Incorporation avoided? All tests	Yes	Reference standard was independent of the index test
Reference standard results blinded? All tests	No	Reference standard interpreted with knowledge of index test results
Index test results blinded? All tests	Yes	Index test interpreted without knowledge of reference standard results
Relevant clinical information? All tests	Yes	Information available as would be in standard clinical practice
Uninterpretable results reported? All tests	Yes	Nasal bones could not be satisfactorily assessed in 6.6% of fetuses
Withdrawals explained? All tests	No	No details of withdrawals given