Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
These concerns need timely assessment but are not always emergencies.
Call emergency services if a baby or child:
Arrange prompt medical advice if a newborn has jaundice, unexplained red or purple skin spots, feeding problems, unusual sleepiness, poor weight gain, or abnormal movements.
If a baby does not pass the newborn hearing screen, arrange the recommended follow-up without delay.
When congenital CMV testing is appropriate, the sample needs to be collected within the first 21 days to confirm that infection occurred before birth.
The article also says
For a child with confirmed congenital CMV, contact the care team if you notice:
Less response to voices or everyday sounds
Loss of words or developmental skills
New problems with balance, movement, feeding, or vision
Unusual staring episodes or repeated jerking movements
Fever or signs of infection while taking antiviral medicine
Every sign above is quoted from the sofidex article on Congenital cytomegalovirus. If you are not sure, err upward — it is always reasonable to be checked.