I got Huey fixed at 6 months and since he is just 7.5 lbs now at 4 years old, he had to be less than or close to 5lbs at that time and he did great. This was my pre-YT days and since this is was the same vet I used for my 100lb lab and had (have) great confidence in, I didn't think to be concerned. Sometimes ignorance is bliss...we did do preop labs etc.