How good is ultrasound prediction of fetal birth weight at term?. Enya Ho Ranen Reddy. Overview:. Audit topic Explanation of standard Method of data collection Data presentation and analysis Case analysis Conclusions Recommendations Suggestions for future study. Aim:.
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Explanation of standard
Method of data collection
Data presentation and analysis
Suggestions for future study
To evaluate the accuracy of Estimated Fetal Weights (EFW) calculated by ultrasound scans done within 7 days of delivery for term [37/40 GA] singleton pregnancies at National Womens Hospital.
Analyse USS data from 2010 with an interval of ≤7 days from scan to delivery.
Identify if the expected standard of care is being met.
Identify and analyse cases that fail to meet the standard.
Identify possible sources of random errors and bias.
Suggest methods for improvement.
“All singleton term pregnancies having an ultrasound-estimated fetal weight within 7 days of delivery achieve a minimal performance of ±15% percentage variation from the fetal birth weight.”
D12 policy on “Performance of 3rd Trimester Ultrasound”under the Australasian Society for Ultrasound in Medicine (ASUM).
Hadlock C-multiparameter formula [based on AC, HC, BPD, and FL] to give the calculated EFW to within 10-15% of the BW, for weights between 1000g and 4000g.
Ultrasound is relatively inaccurate in the assessment of EFW with a mean variation of at least 21% from Birth Weight.
No universal formula to calculate EFW.
AC is the best measure for prediction of EFW, although inter-operator variability exists, particularly for AC estimation.
Most EFW formulae overestimate lower weights and underestimate higher weights.
Target population (n=1897) inclusion criteria:
≥37/40 gestation at delivery
Delivery at NWH
Delivery date in 2010
Sample population (n=120) inclusion criterion : Time interval from ultrasound scan to delivery ≤7 days
AGFA sonography database to gather data for sample population, stratifying data by month and chronology.
(2 BMI not reported)
Data points by BMI:
24 = 39
25-29 = 26
30 = 53
Data points by BW:
2500 = 7
2501-3999 = 94
4000 = 18
Data points by time to del:
0 = 2
1 = 14
2 = 22
3 = 16
4 = 15
5 = 18
6 = 16
7 = 17
BW: 4 cases between 2501-3999g, 1 case 4000g
EFW: 1 case ≤2500g, 2 cases between 2501-3999g, 2 cases 4000g
GDM/Care under maternal diabetes
Limitations of imaging
3 NVDs and 2 LSCSs
-> No obvious causal relationship between percentage error and the factors evaluated in the failed cases could be extrapolated.
96% of scans achieved the accuracy standard set by formula limitation.
Good performance of NWH sonography department.
No obvious causal factors identifiable for large percentage errors.
Suggestion of 1 case where LSCS may have been inappropriate (Case 5).
1. Routine documentation of the expected variability in EFW on USS reports.
2. Documentation of single parameter disproportionality and its effect on reported EFW
3. Ensure clinician awareness of % limitation of EFW.
4. Encourage service user awareness of this % limitation.
5. Regular audit of measurement quality.
1. Use of randomisation for sample population selection.
2. Cross referencing USS reports from Concerto.
3. Frame the current audit to assess different gestations.
4. Frame for assessment of SGA and/or macrosomia.
5. Frame for assessment of patients under MFM.
6. Assess impact of multiple pregnancies in comparison to singleton.
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