I would wait. Many teachers seem to send home a sheet for you to fill out about your child during the first week of school. I took that opportunity to share about my child's abilities. And it became pretty obvious to them quickly, as well.
If there are not earlier opportunities, you can use email to share any pertinent information or share any major issues your child might have (they might not have any) after a couple weeks of school. I tend to ask for a conference a month after school starts since the regular conference time is far too late.
