Cole 1999b.

Clinical features and settings	High‐risk referral for invasive testing.
Participants	1157 participants. USA – 3 hospitals. May 1995 ‐ March 1998. Pregnant women. Singleton pregnancy. 11‐22 weeks' gestation.
Study design	Prospective cohort study.
Target condition and reference standard(s)	Down's syndrome: 23 cases. Reference standards: amniocentesis or CVS.
Index and comparator tests	Urinary hCG beta‐core subunit (B210 2‐step sandwich assay). Urinary total oestriol (radioimmunoassay, kit by Diagnostic Products Corporation, Los Angeles).
Follow‐up	100% karyotyping.
Aim of study	To evaluate use of urinary free beta‐subunit for Down's syndrome screening.
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	Amniocentesis or CVS.
Partial verification avoided? All tests	Yes	All women had a reference standard.
Differential verification avoided? All tests	No	Women had CVS or amniocentesis depending on their stage of pregnancy.
Incorporation avoided? All tests	Yes	Reference standard was independent of the index test.
Reference standard results blinded? All tests	Yes	Reference standard interpreted without 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.