
As always around here

, I'm going against the grain and saying don't bother. You've had 3 matings, albeit slip matings?, Sunday and Monday so that means she should have something there at the 'right time'. Given that sperm can be viable for some while once in the right place. One of mine only ever achieved slips to his bitches, but he only missed to one (given he didn't serve that many bitches). In other words, why not hope some of these 3 matings now, has been successful? I honestly can't see the point having more blood testing done - and you really don't want to be mating her over more than a 48 hours period because it will make knowing her due date, almost impossible to know. And I always go by how my males react in any case, assuming they are experienced stud dogs.
Your decision but that's my response, fwiw.