ad. 13. Ductus venosus – a wave negative (=reversed wave). What does it mean?
Negative “a wave” in the spectral waveform of the flow through ductus venosus (a tiny vessel in a fetal liver accelerating blood flow in the direction of the heart) is an extremely rare ultrasonographic finding. In our records, it occurs in 1.1% of healthy fetuses. In fetuses with genetic syndromes it occurs much more frequently, usually in combination with other genetic markers: in cases of the Down syndrome the negative a wave occurs in 33.3%; of the Edwards syndrome in 54.5%, of the Patau syndrome in 50%, of the Turner syndrome in 22%, basing on our own records.
The problem with examinations in the first trimester is a lot of over-diagnosis. Ductus venosus is a tiny vessel and a fetus is often very active in the first trimester. It is the reason for an increased frequency of an abnormal spectral waveform of the flow through ductus venosus if examined by a less experienced specialist. The assessment and the consultation is even more complicated in case of a fetus with a functional or even an anatomical absence of ductus venosus, frequently observed in children with the genetic risk.
At our centre, if we diagnose a negative “a wave” in ductus venosus together with an increased genetic risk, we recommend a conclusive examination. If the negative a wave does not influence the risk, we recommend an examination of an early fetal anatomy with the assessment of genetic risk and the fetal heart already at 16 weeks of pregnancy.