Summary of findings 3. Accuracy of a single second‐trimester scan in detecting fetal structural anomalies overall, and of varying severity, before 24 weeks' gestation.

Accuracy of a single second‐trimester scan in detecting fetal structural anomalies overall, and of varying severity, before 24 weeks' gestation

Sensitivity

Specificity

Test performance per 100,000 pregnancies

Studies

Fetuses (cases)

Sensitivity (95% CI)

Certainty (GRADE)

Studies

Fetuses (cases)

Specificity (95% CI)

Certainty (GRADE)

Median prevalence (%)

Cases detected (TP)

Cases missed (FN)

True negatives (TN)

False positives (FP)

I. Overall accuracy of ultrasound in detecting fetal structural anomalies

Fetuses affected

9

158,767 (3168)

50.5 (38.5 to 62.4)

Very lowa,b,c

5

33,120 (593)

99.8 (99.2 to 100)

Moderated

2.2**

1115

1094

97,585

205

Anomalies*

3

17,845 (340)

52.2 (33.2 to 70.7)

Very lowa,b,c

‐

‐

‐

‐

4.2**

2194

2006

‐

‐

*No specificity was determined as the number of true negative test results could not be determined by the number of anomalies. **Test performance per 100,000 pregnancies was assessed using the median prevalence of structural anomalies from all studies included in our meta‐analysis on the accuracy of a single second‐trimester scan.

II. Subgroup analysis of ultrasound accuracy in detecting anomalies that are less susceptible to under‐reporting due to incomplete postnatal identification (i.e. anomalies that are externally visible, symptomatic at birth or considered to be lethal)

Fetuses affected

7

58,014 (559)

59.2 (45.7 to 71.5)

Lowb,c

4

32,120 (286)

99.9 (99.6 to 100)

Moderated

1.0**

579

400

98,952

69

III. Accuracy of ultrasound in detecting anomalies of varying severity

Major anomalies

9

75,042 (1312)

47.9 (33.3 to 62.8)

Very lowa,b,c

5

35,124 (469)

99.9 (99.6 to 100)

Moderated

1.3**

625

681

98,635

59

Lethal

7

71,109 (73)

N/A* Range: 80.0 to 100

N/A*

3

31,191 (20)

N/A* Range: 100 to 100

N/A*

0.1**

N/A*

N/A*

N/A*

N/A*

Severe/moderate

8

72,038 (1214)

48.6 (33.0 to 64.5)

Very lowa,b,c

4

32,120 (424)

99.9 (99.3 to 100)

Moderated

1.5**

713

753

98,425

108

Minor anomalies

7

58,015 (96)

24.0 (6.1 to 60.9)

Very lowa,b,e

4

32,120 (82)

N/A* Range: 100 to 100

Moderated

0.3**

79

251

N/A*

N/A*

*Meta‐analysis was not possible because of failure of the random‐effects models to converge due to a lack of variation between studies. **Test performance per 100,000 pregnancies was assessed using the median prevalence of structural anomalies from all studies included in our meta‐analysis on the accuracy of a single second‐trimester scan.

CI: confidence interval; FN: false negative; FP: false positive; N/A: not applicable; TN: true negative; TP: true positive

GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

aContributing studies had design limitations (‐1), including risk of bias in the reference standard domain (‐0.75) and risk of bias in the flow and timing domain (‐0.25). bUnexplained heterogeneity of study results (‐1). cWide 95% CI, deviating more than 10% from the summary estimate (‐1). dContributing studies had design limitations, including risk of partial verification bias of pregnancies due to incomplete verification of ultrasound findings in pregnancies with an adverse outcome (‐1). eWide 95% CI, deviating more than 20% from the summary estimate (‐2).