Hi Sarah,
Thanks for sharing. My six month old is very big too, I rarely meet one bigger (but do occasionally, even among non-CAH), she is 18 lbs and 26.5 inches. She was about 16-17 lbs at 4-5 months. She was born 8.2 lbs at 37 weeks, 3 wks early, I always wondered if it had to do wiht CAH since cortisol inhibits growth hormone, but the Ped Endo said no. I have noticed anecdotaly that many of our babies start to gain fast and eat a lot in the first few months once on meds, but this levels out, and it also seems common that they start off strong and develop fast. My daughter could hold her head up since birth and within 2 weeks she rolled over from her tummy to back. Now she wont roll over hardly at all, she cant move from her back at all, and still doesnt sit up unsupported, overall she’s in the normal range for a baby, but she developed so rapidly at first. I think your son’s size is nothign to worry about (and he is pretty long so he is probably not Cushingoid), but if you are like me you have "baby elbow" from carrying the carseat with him in it!