Matias 1998.

Clinical features and settings	High‐risk referral for invasive testing
Participants	486 participants UK and Portugal Dates not reported Pregnant women Singleton pregnancies Median age 35 years (17‐46 years) 10‐14 weeks' gestation
Study design	Prospective cohort study
Target condition and reference standard(s)	Down's syndrome: 38 cases Reference standard: fetal karyotyping. In cases where NT above 95th percentile or abnormal ductus venousus flow, follow‐up scan conducted at 14‐16 weeks
Index and comparator tests	Maternal age First trimester NT (SSD, Aloka) First trimester ductus venosus flow velocity: measured transabdominally (5‐MHz curvilinear probe, Ecocee, Toshiba) or transvaginally (SSD 2000, Aloka)
Follow‐up	100% karyotyping
Aim of study	To assess the possible role of Doppler ultrasound assessment of ductus venous blood flow in screening for chromosomal abnormalities at 11 to 14 weeks of gestation
Notes
Table of Methodological Quality
Item	Authors' judgement	Description
Representative spectrum? All tests	Yes	Selective testing of high‐risk women as done in practice
Acceptable reference standard? All tests	Yes	Karyotyping
Partial verification avoided? All tests	Yes	All women received a reference standard
Differential verification avoided? All tests	Yes	All women had the same reference standard
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	Reported that measurements made successfully in all cases
Withdrawals explained? All tests	No	No details of withdrawals given