How many tests are too many?

I walked into a conversation today I'm not sure I wanted to have.

Let me back up. Tyler's pedi, Dr. S, is what most would describe as very conservative. His philosophy is, "Better test than sorry." So when Tyler's head got bigger and bigger (it jumped 45 percentile points in about six months), he ordered a CT scan. Everything turned out fine, thank God.

At Tyler's 9-month appointment last week, Tyler had only gained a bit of weight, and hadn't grown in length at all. Acknowledging that there is a margin for error in length measurement, the doc asked him to come back in six weeks for another measure. There could be a thyroid problem, he explained. How things have changed for me. Rather than immediately panicking about my son's thyroid, my first thought was, man, now I have to pay another co-pay.

I shared this news with my friend A, whose daughter also sees Dr. S. She nodded and said she has been considering finding another pedi. They pay for their own insurance and have a high deductible, so they pay $200 for each visit. Dr. S just ordered a bunch of tests, including lead, for her daughter's 12-month and after talking to friends, she doesn't feel the tests are necessary (mother's intuition).

Though I was the one who started the conversation, I found myself bristling. The dead-baby mama in me wanted to shout, "But we did have the worst-case scenario once! How can you just assume everything is fine? I'll tell you how--because nothing bad has ever happened to you!"

Yet, another part of me just doesn't know. How do you draw the line between being responsible and being overcautious?