Crossley 2002.

Clinical features and settings	Routine screening
Participants	17,229 participants UK ‐ 15 centres Dates not specified Pregnant women Median age 29.9 years, 15.4% ≥ 35 years 10‐14 weeks' gestation
Study design	Prospective cohort
Target condition and reference standard(s)	Down’s syndrome: 45 cases Reference standards: CVS (offered where women had high NT measurements), amniocentesis or follow‐up to birth
Index and comparator tests	Maternal age NT (FMF method) in 73% of patients Clotted blood samples tested for: Free ßhCG and PAPP‐A (Kryptor analyser) in 98.4% of patients
Follow‐up	Reported that the outcome of all pregnancies was followed up
Aim of study	To evaluate the use of NT measurement in combination with biochemical markers as a first trimester test for Down's syndrome in routine antenatal setting
Notes
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	Report average success rate of NT (72.9%)
Withdrawals explained? All tests	Yes	Numbers of patients not undergoing NT and biochemical testing given