This is a late answer but for someone who might read this in the future we will post it anyway. The risk is much higher to the animal and it certainly raises the risk the animal bleeding out. There is also more swelling. We were going to have our Show Basenji spayed this year. She went into heat slightly early and our vet said that we should wait until after the heat was over before he felt comfortable doing the spay for the reasons mentioned.
Service Veterinary Clinics - Spaying and Neutering
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As a common rule, citizens go to a veterinary clinic to vaccinate their pets, prove for pathological, daily checkups, poor health and sickness that drop within ordinary clinical cases.
https://medium.com/@paullopez03/common-misconceptions-regarding-spaying-and-neutering-7cd2312f0596#.8qjtx9544
