It depends on what hormone tests they are running on your child.
A Total T4 test will not show a problem.
A Total T3 test wil not show a problem.
Free T4 tests and Free T3 tests are much more acurate. Even so, the lab range for these tests is so broad that your tests can come back "normal" even though the hormone being measured is high or low.
As long as these tests come back "within lab limit", many doctors will not look at the numbers and see a problem. But you can be hypo or hyper and have Free T tests come back within limits.
Another isue is antibodies. If your child has TRab (an antibody), the TSH will rise even though the hormone levels are good.
Yet a third possibility is a pituitary problem that causes over-production of TSH.
So you need to get copies of all the test results and find out if there is a hormone deficiency or not. Just because the tests says half a point above lower limit is normal does not make it true.
The thyroid is a complete mystery for many doctors & patients. According to my doctor, thyroid levels can fluctuate daily for no reason, the thyroid is a mystery gland.
I am a perfect example. In the past 2.5 years, all my thyroid labs returned normal, just recently a thyroid uptake scan, revealed I am chronically hyperthyroid, although my labs the day before returned normal.
Diagnosing a thyroid takes time, and alot of patients. In time, you will have answers and a stable treatment for your son.
Good luck to you, and a warm hug to your newborn.