I think that the studying I had to do for my degree (Family and Child Development) plus 10+ years in the ECE profession has beaten the competative/comparer out of me.
For one thing, I know that most parenting books are full of absolute unadulterated crap as far as the 'spread' of what kids should be doing cognitively/developmentally. There are even some pedatricians I've met that are overly alarmist (or not enough). For another, I have seen so many kids that were 'slow' in my lifetime that were absolutely brilliant, just needed some time to come out of their shell. And kids who were 'ahead' but by the time they were school age some major problems started arising that needed to be dealt with but *weren't* because their families were so proud of the 'bright' status that they couldn't or wouldn't see the problems. Most kids are just fine and develop on their own timelines. Some kids get unfairly penalized and unfairly compared because people think they're younger/older than they are (due to size) and treat them accordingly.
Except for my circle of closeknit internet friends, I don't really have many other moms in my circle. Because I don't have as much investment in friendship as far as the really competative/comparative moms I DO know, when they start playing that game, it's easy for me to ignore. Though if anyone ever started criticizing my child (and they were totally off base) they would be out of my life SO fast! Our family leads a slow, uncomplicated life...I just don't relate to people who push push push or need to be the best in everything. (Just wait, one of my kids will probably have an inborn trait that makes them do this--eep!) I think it's easier for me to shrug things off because I know better than most people who think of children as some sort of developmental race or praise-winning devices (esp. if they're just getting their info out of parenting magazines...you guys know the ones I'm talking about). I love keeping up with the latest brain research, ect...but I know how to translate that into RL, and not get bogged down on what part of the scale my little girl is.
I think eventually that if you're confident in your child, and you decide that you'll let her grow at her own pace that you'll either grow a thicker skin as far as other people looking at her/him in that way, or you'll grow very impatient with people with a competative agenda. Or probably both. It's okay to worry about your kid...who doesn't?!?! Just try to worry about them in the context that you notice something is 'off' about them, that they're slowing down or having some difficulties in certain areas, ect...contextualize it to THEM, not to other children. I know that's hard to do, but it can be done.