I have a little yorkie. Debbie was just about 7 months old and weighed 2.7 pounds when I had her spayed. Since then she's been put under two more times for baby teeth removal and then teeth cleaning last year. Knock wood but she's always been fine so far. Try to find a vet who is knowledgeable about tiny dogs.
We lost a big yorkie to pyometra many years ago because we didn't know any better. She required a hysterectomy and I never wanted to go through something like that again. The more times your dog goes into heat, the greater the chance of her contracting this disease.
http://www.marvistavet.com/html/body_pyometra.html