Hello, In most cases with normal development, outcome is good. Risk increases if there are any chromosomal anomalies associated or other birth defects are detected.
In your case there has been no evident anomaly detected by ultrasound, so after delivery the baby will have to be assessed for chromosomal and other anomalies.
In few such cases there may be enlargement of baby's heart, but this is not case with you so the outlook looks OK.
Cause of this anomaly is unknown.
Is there an increased risk for brain damage or cerebral palsy as a result of the umbilical vein dilation/umbilical vein varix?
At this point, I am concerned about the overall outcome and development, if there have been issues with the blood and oxygen flow due to the umbilical vein varix.
Brain development is not directly affected because varix can cause only heart problem due to circulatory effect, like blood stasis. Overall good growth and development so far indicates that circulation has not been compromised so no oxygen lack to brain is likely.