O'Callaghan 2000.

Clinical features and settings	Routine screening
Participants	1000 participants Australia ‐ public and private sector venues September 1997 to September 1999 Pregnant women Singleton or multifetal pregnancies (2000 fetuses including 25 sets of dichorionic twins, 7 sets of monochorionic twins and 4 sets of triplets but the numbers amongst the 1000 fetuses reported in the paper were not stated) Median age 32 years 11‐14 weeks' gestation
Study design	Prospective cohort
Target condition and reference standard(s)	Down’s syndrome: 8 cases Reference standards: CVS, amniocentesis, neonatal karyotyping or follow‐up to birth
Index and comparator tests	Maternal age NT (FMF methods)
Follow‐up	Follow‐up from cytogenetics laboratory records but the completeness of follow‐up is not reported
Aim of study	To evaluate a risk assessment tool based on first trimester NT
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	Unclear	Unclear if all women had a reference standard
Differential verification avoided? All tests	Unclear	Unclear if the 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	No	No details given for test failures/uninterpretable measurements
Withdrawals explained? All tests	No	No details of withdrawals given