Sensitivity analyses
	Fetuses affected		Anomalies
	Studies	Sensitivity (95% CI)	Studies	Sensitivity (95% CI)
First‐trimester scan
Summary estimate of all included studies	20	37.5 (31.1 to 44.3)	20	39.2 (32.5 to 46.2)
Summary estimate of studies that reported complete 2 x 2 tables	10	35.5 (27.0 to 45.0)	9	36.7 (26.2 to 48.6)
Summary estimate of studies at low risk of bias ‐ patient selection	17	35.1 (28.6 to 42.2)	17	37.4 (30.1 to 45.3)
Summary estimate of studies with low applicability concerns ‐ patient selection	4	N/A*	3	N/A*
Summary estimate of studies at low risk of bias ‐ index test	20	37.5 (31.1 to 44.3)	20	39.2 (32.5 to 46.2)
Summary estimate of studies with low applicability concerns ‐ index test	16	40.3 (32.9 to 48.2)	16	42.4 (35.3 to 49.9)
Summary estimate of studies at low risk of bias ‐ reference standard	2	N/A*	2	N/A*
Summary estimate of studies with low applicability concerns ‐ reference standard	20	37.5 (31.1 to 44.3)	20	39.2 (32.5 to 46.2)
Summary estimate of studies at low risk of bias ‐ flow and timing	1	N/A*	1	N/A*
Summary estimate, excluding studies that used data obtained from birth defect registries	20	37.5 (31.1 to 44.3)	20	39.2 (32.5 to 46.2)
Summary estimate, excluding studies with fewer than 10 cases that had the target condition	17	37.6 (30.9 to 41.6)	18	39.3 (32.4 to 46.5)
Summary estimate, excluding studies with ≥ 10% lost to follow‐up	15	36.6 (29.1 to 44.7)	15	36.9 (29.0 to 45.5)
First + second‐trimester scan
Summary estimate of all included studies	18	83.8 (74.7 to 90.1)	17	84.5 (75.8 to 90.5)
Summary estimate of studies that reported complete 2 x 2 tables	10	82.6 (71.2 to 90.1)	8	84.0 (71.9 to 91.6)
Summary estimate of studies at low risk of bias ‐ patient selection	15	82.4 (71.7 to 89.7)	14	83.0 (72.7 to 90.0)
Summary estimate of studies with low applicability concerns ‐ patient selection	4	N/A*	3	N/A*
Summary estimate of studies at low risk of bias ‐ index test	18	83.8 (74.7 to 90.1)	17	84.5 (75.8 to 90.5)
Summary estimate of studies with low applicability concerns ‐ index test	16	82.6 (72.3 to 89.7)	15	83.3 (73.3 to 90.1)
Summary estimate of studies at low risk of bias ‐ reference standard	2	N/A*	2	N/A*
Summary estimate of studies with low applicability concerns ‐ reference standard	18	83.8 (74.7 to 90.1)	17	84.5 (75.8 to 90.5)
Summary estimate of studies at low risk of bias ‐ flow and timing	1	N/A*	1	N/A*
Summary estimate, excluding studies that used data obtained from birth defect registries	18	83.8 (74.7 to 90.1)	17	84.5 (75.8 to 90.5)
Summary estimate, excluding studies with fewer than 10 cases that had the target condition	15	83.4 (73.3 to 90.2)	15	84.4 (74.9 to 90.8)
Summary estimate, excluding studies with ≥ 10% lost to follow‐up	14	84.3 (74.5 to 90.8)	14	85.2 (76.0 to 91.3)
Single second‐trimester scan
Summary estimate	9	50.5 (38.5 to 62.4)	3	52.2 (33.2 to 70.7)
Summary estimate of studies that reported complete 2 x 2 tables	5	59.3 (42.4 to 74.2)	N/A*	N/A*
Summary estimate of studies at low risk of bias ‐ patient selection	7	52.5 (38.6 to 66.1)	N/A*	N/A*
Summary estimate of studies with low applicability concerns ‐ patient selection	8	53.2 (40.8 to 65.2)	N/A*	N/A*
Summary estimate of studies at low risk of bias ‐ index test	9	50.5 (38.5 to 62.4)	N/A*	N/A*
Summary estimate of studies with low applicability concerns ‐ index test	9	50.5 (38.5 to 62.4)	N/A*	N/A*
Summary estimate of studies at low risk of bias ‐ reference standard	4	N/A*	N/A*	N/A*
Summary estimate of studies with low applicability concerns ‐ reference standard	9	50.5 (38.5 to 62.4)	N/A*	N/A*
Summary estimate of studies at low risk of bias ‐ flow and timing	1	N/A*	N/A*	N/A*
Summary estimate, excluding studies that used data obtained from birth defect registries	8	52.2 (33.2 to 70.6)	N/A*	N/A*
Summary estimate, excluding studies with fewer than 10 cases that had the target condition	9	50.5 (38.5 to 62.4)	N/A*	N/A*
Summary estimate, excluding studies with ≥ 10% lost to follow‐up	9	50.5 (38.5 to 62.4)	N/A*	N/A*
*N/A: sensitivity analysis was not performed if four or fewer studies were available.