Borenstein 2008.

Clinical features and settings	High‐risk referral for invasive testing
Participants	516 participants London ‐ hospital birth centre Dates not reported Pregnant women Median maternal age 35 years (range 17‐49 years) 11‐13 weeks' gestation 16‐24 weeks' gestation in a sub‐sample of 183 women
Study design	Prospective cohort
Target condition and reference standard(s)	Down's syndrome: 51 cases Reference standard: CVS
Index and comparator tests	First trimester fetal echocardiography (transabdominally with a 4‐8 MHz curvilinear transducer, Voluson 730 Expert, GE Medical Systems) in all women (425 successfully examined) and in the second trimester in 183 women
Follow‐up	100% karyotyping
Aim of study	To establish the feasibility of examining the subclavian artery at 11 + 0 to 13 + 6 weeks of gestation and to determine the prevalence of aberrant right subclavian artery (ARSA) in chromosomally normal and abnormal fetuses
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
Partial verification avoided? All tests	Yes	All women received a reference standard
Differential verification avoided? All tests	Yes	All women received 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	425/516 (82.4%) of women were successfully examined
Withdrawals explained? All tests	No	No details of withdrawals given