Cicero 2004a.

Clinical features and settings	High‐risk referral for invasive testing
Participants	970 fetuses (20 twin and 1 triplet pregnancy) UK Dates not specified Pregnant women Median age 37 years (16‐48 years) 11‐14 weeks' gestation (median 12 weeks)
Study design	Prospective cohort study
Target condition and reference standard(s)	Down's syndrome: 88 cases Reference standard: CVS
Index and comparator tests	Maxillary bone length Mid‐saggital view of fetal profile obtained for nasal bone. Transducer angled laterally so that the maxillary bone and mandible including the ramus and condylar process can be seen. Maxillary length measured with callipers. Magnified to 0.1 mm increment
Follow‐up	100% karyotyping
Aim of study	To determine the value of measuring maxillary length at 11‐14 weeks' gestation in screening for trisomy 21
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	CVS
Partial verification avoided? All tests	Yes	All women had 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	Study reports that measurements were made successfully in all cases
Withdrawals explained? All tests	No	No details of withdrawals given