Zhang 2021.

Study characteristics
Patient Sampling	Study design: population‐based retrospective cohort study Recruitment: data obtained from the birth defect surveillance system in Beijing. A birth defect registration card was used by medical staff for data collection in the surveillance hospitals, and the information for women and their babies, birth defect diagnosis and pregnancy test results were obtained from clinical records, all of which were available online. Study start and end date: 2018 to 2020
Patient characteristics and setting	Setting: the birth defect surveillance system in Beijing, covering all regions of Beijing and including all midwifery hospitals in the region Region(s) and country/countries from which participants were recruited: Beijing, China Sample size: 594,860 Study eligibility criteria: all cases with congenital heart defects reported to the birth defect registry Number of participants with the target condition: 5501 Population type: unselected population Prior testing: a first‐trimester scan was performed at 11 to 13 weeks' gestation; purpose and protocol for the first‐trimester scan not specified
Index tests	Type: single‐stage screening Second‐trimester scan: Timing: 20 to 24 weeks’ gestation Ultrasound scanning protocol: not reported Cardiac screening: not reported Mode of examination: not reported Single or multiple operators: multiple Staff qualification and/or operator experience level: not reported
Target condition and reference standard(s)	Target condition(s): cardiac anomalies (any type) Definitions used for major and minor congenital abnormalities: cardiac anomalies were classified as simple or critical congenital heart defects. Simple congenital heart defects refer to a single defect that generally does not cause haemodynamic changes. This category included patent ductus arteriosus > 3 mm and atrial septal defects > 3 mm. Critical congenital heart defects were defined according to the Centers for Disease Control and Prevention standards, namely persistent truncus arteriosus, double‐outlet right ventricle, d transposition of the great vessels, single ventricle, tetralogy of Fallot, pulmonary valve atresia, Ebstein malformation, tricuspid atresia, hypoplastic left heart syndrome, coarctation of the aorta, interrupted aortic arch and total anomalous pulmonary venous return. Reference standard (live birth): pregnancy and neonatal outcome were obtained from hospital records Reference standard (fetal or neonatal demise): not reported Postnatal follow‐up duration: not reported
Flow and timing	Eligible patients: 594,860 Exclusions (study investigator): none reported Exclusions (review team): 383 (cases with a congenital heart defect who did not receive 20‐ to 24‐week ultrasound screening)
Comparative
Notes	A first‐trimester scan was performed at 11 to 13 weeks' gestation. Purpose and scanning protocol were not reported. We classified the study as having a single‐stage screening approach under the assumption that the 11‐ to 13‐week scan did not include complete examination of the fetal anatomy. Funding source: this work was supported by the National Key R&D Program of China (2018YFC1002304)
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
Did the study avoid inappropriate exclusions?	Yes
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index Test (First‐trimester scan)
DOMAIN 2: Index Test (First + second‐trimester scan)
DOMAIN 2: Index Test (Single second‐trimester scan)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
If a threshold was used, was it pre‐specified?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference Standard
Is the reference standard likely to correctly classify anomalies that are externally visible, present with clinically relevant symptoms shortly after birth, or that are considered to be lethal/incompatible with life?	Yes
Is the reference standard likely to correctly classify anomalies that may present after discharge from postnatal care?	Unclear
Were the reference standard results interpreted without knowledge of the results of the index test?	No
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and Timing
Did all live‐born infants receive a reference standard?	Yes
Did all live‐born infants receive the same reference standard?	No
Did all cases of fetal or perinatal loss receive the reference standard (including termination of pregnancy, intra‐uterine death, stillbirth, perinatal mortality)?	Unclear
Were all patients included in the analysis?	Yes
Could the patient flow have introduced bias?		Unclear risk