Nicolaides 1992.

Clinical features and settings	High‐risk referral for invasive testing
Participants	827 participants UK ‐ research centre for fetal medicine January 1990 ‐ October 1991 Pregnant women Median age 38 years (22‐47 years) 10‐14 weeks' gestation
Study design	Prospective cohort
Target condition and reference standard(s)	Down's syndrome: 13 cases Reference standards: fetal karyotyping by amniocentesis (52%) or CVS (48%)
Index and comparator tests	Maternal age First trimester NT (curvilinear 5MHz transducer, Aloka 650 CO Limited)
Follow‐up	100% karyotyping
Aim of study	To examine the significance of fetal NT at 10‐14 weeks' gestation in the prediction of abnormal fetal karyotype
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 different reference standards
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