Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for:
Emergency care is needed for acute medical or safety problems.
If you drink heavily or develop withdrawal symptoms when you stop, get medical advice promptly.
Arrange a routine appointment if a child has persistent concerns involving growth, learning, attention, coordination, communication, or behavior.
Assessment may be appropriate when prenatal alcohol exposure is known or suspected, although these concerns can have other causes.
Seek routine follow-up for worsening school performance, sleep problems, anxiety, low mood, hearing or vision concerns, or difficulty with everyday tasks.
Adults who think a diagnosis was missed can ask about developmental, neuropsychological, or FASD assessment.
The article also says
If you are pregnant and drinking alcohol, contact a prenatal care or addiction service.
Seeking help early can reduce further exposure.
FAS itself is not usually an emergency.
Every sign above is quoted from the sofidex article on Fetal alcohol syndrome. If you are not sure, err upward — it is always reasonable to be checked.