Ductus venosus flow

 

11-13 week scan
Ductus venosus flow

FMF Certificate of competence in assessment of ductus venosus flow

The findings of recent studies suggest that examination of the ductus venosus waveform at 11-13 weeks could have major beneficial implications in screening for both chromosomal abnormalities and major cardiac defects.

The FMF software which allows calculation of risk for both chromosomal and cardiac defects is provided free of charge to sonographers who have been appropriately trained and accredited in the assessment of the fetal ductus venosus flow.

Requirements for Certification in assessment of ductus venosus flow

The requirements for certification are:

1. FMF certification in measurement of nuchal translucency.
2. Attendance of the internet based course on the 11-13 weeks scan.
3. Submission of a logbook of 3 images including two with positive and one with reversed a-wave at 11-13 weeks.

Protocol for the assessment of the ductus venosus

• The gestational period must be 11 to 13 weeks and six days.
• The examination should be undertaken during fetal quiescence.
• The magnification of the image should be such that the fetal thorax and abdomen occupy the whole image.
• A right ventral mid-sagittal view of the fetal trunk should be obtained and color flow mapping should be undertaken to demonstrate the umbilical vein, ductus venosus and fetal heart.
• The pulsed Doppler sample volume should be small (0.5 mm) to avoid contamination from the adjacent veins, and it should be placed in the yellowish aliasing area.
• The insonation angle should be less than 30 degrees.
• The filter should be set at a low frequency (50-70 Hz) so that the a-wave is not obscured.
• The sweep speed should be high (2-3 cm/s) so that the waveforms are spread allowing better assessment of the a-wave.
• When these criteria are satisfied, it is possible to assess the a-wave and determine qualitatively whether the flow is positive, absent or reversed.

Clinical application of ductus venosus flow findings

The incidence of reversed ductus venosus a-wave is related to NT and CRL as well as aneuploidy, being more common when the NT is high and the CRL is low. Therefore it is not possible to give simple numbers by which the presence of normal flow will reduce the risk for trisomy 21 and the presence of reversed a-wave will increase the risk.

The FMF software firstly calculates a risk based on maternal age, fetal NT and maternal serum free ß-hCG and PAPP-A. If the risk is more than 1 in 50 and ductus venosus flow is normal the risk does not change. If the risk is 1 in 50 to 1 in 1,000 and the ductus venosus flow is normal the risk is usually reduced. If there is reversed a-wave the risk is always increased. In addition, there is an increased risk for cardiac defects and therefore such patients should have a follow up specialist fetal cardiac scan.

Submission of logbook

Postive a-wave

Reversed a-wave