Increased impedance to flow in the fetal ductus venosus at 11-13 weeks’ gestation, is associated fetal aneuploidies, cardiac defects and other adverse pregnancy outcomes. Most studies examining ductus venosus flow have classified the waveforms as normal, when the a-wave observed during atrial contraction is positive, or abnormal, when the a-wave is absent or reversed. The preferred alternative in the estimation of patient-specific risks for pregnancy complications is measurement of the pulsatility index for veins (PIV) as a continuous variable.
Inclusion of ductus venosus blood flow in first-trimester combined screening improves the detection rate for trisomy 21 from about 90% to 95% for a false positive rate of 3%. Assessment of ductus venosus flow need not be carried out in all pregnancies undergoing routine first-trimester combined screening. Such examination could be reserved for the 15% of the total population with an intermediate risk (between 1 in 51 and 1 in 1000) after combined testing.
Requirements for certification
The requirements for obtaining the FMF certificate of competence in assessment of ductus venosus flow are:
- Attendance of the internet based course on the 11-13 weeks scan.
- FMF certification in measurement of nuchal translucency.
- Successful completion of a short online test in which you will be asked to examine images on assessment of ductus venosus flow.
- Submission of a logbook of 3 images showing correct assessment of ductus venosus flow.
Protocol for assessment
- 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 (0.5-1.0 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.
- The ductus venosus PIV is measured by the machine after manual tracing of the outline of the waveform.
Color Doppler of Ductus venosus
Quality review and ongoing certification
- Sonographers who have obtained the Certificate of competence in the assessment of ductus venosus flow need to pass an audit on an annual basis.
- The audit involves (a) successful completion of a short online test in which you will be asked to examine images on assessment of ductus venosus flow and (b) submission of a logbook of 3 images showing correct assessment of ductus venosus flow.
- The date and time of the scan should always be clearly visible on each submitted image. If possible, please also include the name of your hospital. Cases older than the last audit will not be accepted.
- Sonographers who pass their audit will receive renewal of their licence for one year and their name will be published on the FMF website list of holders of the Certificate of competence in assessment of ductus venosus flow.
- Sonographers who fail their audit will not receive renewal of their licence and their name will be removed from the FMF website list of holders of the Certificate of competence in assessment of ductus venosus flow.