I've been transferring IVF embryos (various breeds) for almost 5 years. I personally prefer frozen embryos versus the fresh because my conception rate has been so good. Using frozens allows me to calf certain matings throughout the year instead of all hitting at the same time from a fresh...
Not saying the blood test would cause to abort but what do you do with the females that are open? Most breeders set those females back up and generally use lute or Estrumate which can abort a pregnancy during the first 100 days. I have seen too many false positives/false negatives and...
Personally I prefer to have my recips confirmed via ultrasound so I can see the heartbeat. If seen people abort pregs from blood checks and palpations. I think the average loss after 60 days is around 5-7% but recips maintenance is vital.
I have been putting in fresh & frozen IVF embryos for last 4 1/2 years. You hear that fresh is best but I've had a lot of success with frozen. The freezing techniques have been tested and the company I use had hard data to support the freeze methods.