One of my Yorkies was spayed after her first heat, and I worried it could affect her health. She lived a month shy of seventeen. From what I know now, I would wait until after the growth plates have closed. You should wait until he adult teeth come in so your vet can pull the baby teeth that don't come out on their own. Once more doctors start doing tubal ligations, I would probably look intro that so that the hormones remain. The risk of pyrometra in. unspayed females is high, but with tubal ligation and spayed females it's not something to worry about.
http://www.caninesports.com/uploads/...tions_2013.pdf